Rach conveyance of dl synchronization beam information for various dl-ul correspondence states

ABSTRACT

Methods, systems, and devices for wireless communication are described. A user equipment (UE) may receive a downlink (DL) signal from a base station on one or more DL beam(s). The UE may identify a selected DL beam of the one or more DL beam(s) for communications from the base station to the UE. The UE may transmit a beam recovery or beam tracking message to the base station using at least one of a resource or a waveform selected based at least in part on the selected DL beam.

CROSS REFERENCES

The present application for patent claims priority to U.S. ProvisionalPatent Application No. 62/374,735 by Islam, et al., entitled “RACHConveyance of DL Synchronization Beam Information For Various DL-ULReciprocity States,” filed Aug. 12, 2016 and to U.S. Provisional PatentApplication No. 62/379,209 by Islam, et al, entitled “RACH Conveyance ofDL Synchronization Beam Information For Various DL-UL ReciprocityStates,” filed Aug. 24, 2016 and to U.S. Provisional Patent ApplicationNo. 62/406,377 by Islam, et al., entitled “RACH Conveyance of DLSynchronization Beam Information For Various DL-UL Reciprocity States,”filed Oct. 10, 2016, and to U.S. Provisional Patent Application No.62/407,423 by Islam, et al., entitled “RACH Conveyance of DLsynchronization Beam Information For Various DL-UL Reciprocity States”filed Oct. 12, 2016 and to U.S. Provisional Patent Application No.62/418,072 by Islam, et al., entitled “RACH Conveyance of DLSynchronization Beam Information For Various DL-UL Reciprocity States,”filed Nov. 4, 2016 and assigned to the assignee hereof.

BACKGROUND

The following relates generally to wireless communication, and morespecifically to random access channel (RACH) conveyance of downlink (DL)synchronization beam information for various downlink-uplink (DL-UL)correspondence states.

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., time, frequency, and power). Examples of suchmultiple-access systems include code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, and orthogonal frequencydivision multiple access (OFDMA) systems, (e.g., a Long Term Evolution(LTE) system). A wireless multiple-access communications system mayinclude a number of base stations, each simultaneously supportingcommunication for multiple communication devices, which may be otherwiseknown as user equipment (UE).

Wireless communication systems may operate in millimeter wave (mmW)frequency ranges, (e.g., 28 GHz, 40 GHz, 60 GHz, etc.). Wirelesscommunications at these frequencies may be associated with increasedsignal attenuation (e.g., path loss), which may be influenced by variousfactors, such as temperature, barometric pressure, diffraction, etc. Asa result, signal processing techniques, such as beamforming, may be usedto coherently combine energy and overcome the path losses at thesefrequencies. Due to the increased amount of path loss in mmWcommunication systems, transmissions from the base station and/or the UEmay be beamformed.

Wireless communications between two wireless nodes, (e.g., between abase station and a UE), may use beams or beam-formed signals fortransmission and/or reception. A base station may transmit beamformedsynchronization signals on downlink (DL) synchronization beams. A UE mayreceive a synchronization signal on one or more of the DLsynchronization beams, and thus be enabled to initiate a RACH procedurewith the base station. In some instances, the UE may send a message tothe base station as part of the RACH procedure, and the base station mayassume that the uplink (UL) beam on which the RACH message is receivedis representative of a DL beam which the base station should use incommunicating with the UE. In other words, the base station assumesDL-UL correspondence. However, correspondence between the DL channel andUL channel may be missing, for various reasons. Thus, the base stationassumption may be incorrect, meaning that the DL beam selected by thebase station may not be the most appropriate beam for communicationswith the UE.

SUMMARY

The described techniques relate to improved methods, systems, devices,or apparatuses that support RACH conveyance of DL beam information forvarious DL-UL correspondence states. Generally, the described techniquesprovide for a base station to transmit DL signals to a UE. The DLsignals may be transmitted on DL beam(s). The UE may use the DL beamfrom the DL beam(s) that can be used for communicating with the basestation, (e.g., DL communications). The UE may select a resource and/ora random access channel (RACH) waveform for transmission of a RACHmessage, (e.g., RACH msg1, to the base station). In some aspects, the UEmay select the resource and/or the waveform based on the DL beam. The UEmay transmit the RACH message to the base station on the selectedresource and/or the waveform. The base station may receive the RACHmessage on the resource and/or the waveform and identify the DL beamselected by the UE based on the resource and/or the waveform. The basestation may use the selected DL beam for subsequent communications withthe UE.

A method of wireless communication is described. The method may includereceiving a DL signal from a base station on one or more DL beams,identifying a selected DL beam of the one or more DL beams forcommunications from the base station to the UE, and transmitting a RACHmessage/scheduling request message/beam recovery or beam trackingmessage to the base station using at least one of a resource or awaveform selected based at least in part on the selected DL beam.

An apparatus for wireless communication is described. The apparatus mayinclude means for receiving a DL signal from a base station on one ormore DL beams, means for identifying a selected DL beam of the one ormore DL beams for communications from the base station to the UE, andmeans for transmitting a RACH message/scheduling request message/beamrecovery or beam tracking message to the base station using at least oneof a resource or a waveform selected based at least in part on theselected DL beam.

Another apparatus for wireless communication is described. The apparatusmay include a processor, memory in electronic communication with theprocessor, and instructions stored in the memory. The instructions maybe operable to cause the processor to receive a DL signal from a basestation on one or more DL beams, identify a selected DL beam of the oneor more DL beams for communications from the base station to the UE, andtransmit a RACH message/scheduling request message/beam recovery or beamtracking message to the base station using at least one of a resource ora waveform selected based at least in part on the selected DL beam.

A non-transitory computer readable medium for wireless communication isdescribed. The non-transitory computer-readable medium may includeinstructions operable to cause a processor to receive a DL signal from abase station on one or more DL beams, identify a selected DL beam of theone or more DL beams for communications from the base station to the UE,and transmit a RACH message/scheduling request message/beam recovery orbeam tracking message to the base station using at least one of aresource or a waveform selected based at least in part on the selectedDL beam.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the waveform comprises one ofa scheduling request or a random access channel (RACH) waveform.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the DL signal comprises asynchronization signal or a reference signal.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the selected resource orwaveform comprises: selecting the resource or the waveform based atleast in part on an index of the selected DL beam. In some examples ofthe method, apparatus, and non-transitory computer-readable mediumdescribed above, the selected resource or waveform comprises: selectingthe resource or the waveform based at least in part on a symbol of asubframe of the DL signal of the selected DL beam.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, transmitting the RACHmessage/scheduling request message/beam recovery or beam trackingmessage comprises: transmitting the RACH message/scheduling requestmessage/beam recovery or beam tracking message during an entire durationof a corresponding random access subframe. In some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove, identifying the selected DL beam comprises: identifying apreferred DL beam based at least in part on a signal strength of the DLsignal on the one or more DL beams, a signal quality of the DL signal onthe one or more DL beams, or combinations thereof.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, identifying the selected DLbeam comprises: identifying the DL beam based at least in part on the DLsignal on the one or more DL beams meeting a transmit power condition.Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for selecting the resource or thewaveform for transmission of the RACH message/scheduling requestmessage/beam recovery or beam tracking message to the base station, theresource or waveform being selected based at least in part on theselected DL beam.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, selecting the waveformcomprises: selecting a RACH preamble, a cyclic shift, or combinationsthereof based at least in part on an index of the selected DL beam. Insome examples of the method, apparatus, and non-transitorycomputer-readable medium described above, a correspondence is absentbetween the one or more DL beams and one or more uplink (UL) receivebeams at the UE, wherein the absent correspondence is associated withthe one or more DL beams having different beam directions than the oneor more UL beams.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying that correspondence isabsent between the one or more DL beams from the base station and one ormore uplink (UL) receive beams at the base station by receivinginformation from the base station in a master information block (MIB) ora system information block (SIB). Some examples of the method,apparatus, and non-transitory computer-readable medium described abovemay further include processes, features, means, or instructions fortransmitting the RACH message/scheduling request message/beam recoveryor beam tracking message to the base station during an entire durationof a RACH subframe based at least in part on the identification of theabsent correspondence. Some examples of the method, apparatus, andnon-transitory computer-readable medium described above may furtherinclude processes, features, means, or instructions for selecting theresource or waveform based at least in part on the identification of theabsent correspondence.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving the indication of theabsent correspondence in a master information block (MIB) or a systeminformation block (SIB). Some examples of the method, apparatus, andnon-transitory computer-readable medium described above may furtherinclude processes, features, means, or instructions for transmitting anindication that correspondence is absent between the one or more DLbeams from the base station and one or more UL beams at the UE. Someexamples of the method, apparatus, and non-transitory computer-readablemedium described above may further include processes, features, means,or instructions for transmitting the RACH message/scheduling requestmessage/beam recovery or beam tracking message to the base stationduring a first symbol of a first random access subframe and a secondsymbol of a second random access subframe. Some examples of the method,apparatus, and non-transitory computer-readable medium described abovemay further include processes, features, means, or instructions fortransmitting the indication of the absent correspondence in a RACHmessage 3, a physical uplink control channel (PUCCH), or a physicaluplink shared channel (PUSCH).

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving an indication of a natureof correspondence between the one or more DL beams at the base stationand one or more uplink (UL) beams at the base station, wherein thenature of correspondence corresponds to one of: full correspondence,partial correspondence, or no correspondence.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining that correspondence ispresent based on the indication of the nature of correspondence andselecting a transmission time for transmitting the RACHmessage/scheduling request message/beam recovery or beam trackingmessage to the base station based on the present correspondence. In someexamples, the transmission time includes a symbol of a correspondingrandom access subframe. Some examples of the method, apparatus, andnon-transitory computer-readable medium described above may furtherinclude processes, features, means, or instructions for determining thatthere is partial correspondence based on the indication of the nature ofcorrespondence and selecting a transmission time for transmitting theRACH message/scheduling request message/beam recovery or beam trackingmessage to the base station based on the partial correspondence. In someexamples, the transmission time includes multiple symbols of acorresponding random access subframe.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for selecting a transmission time, afrequency range, and a RACH preamble for transmitting the RACHmessage/scheduling request message/beam recovery or beam trackingmessage based on the nature of correspondence. Some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove may further include processes, features, means, or instructionsfor selecting the resource or waveform based at least in part on asymbol associated with the DL signal and the indication of the nature ofcorrespondence. Some examples of the method, apparatus, andnon-transitory computer-readable medium described above may furtherinclude processes, features, means, or instructions for receiving theindication of the nature of correspondence over a physical broadcastchannel (PBCH) or an extended PBCH (ePBCH). Some examples of the method,apparatus, and non-transitory computer-readable medium described abovemay further include processes, features, means, or instructions forreceiving the indication of the nature of correspondence in a MIB or aSIB.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the selected DL beam from thebase station may be different from a selected UL beam from the UE. Insome examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the one or more DL beams maybe within a single symbol of a synchronization subframe, whereinselecting the resource or the waveform for transmission of the RACHmessage/scheduling request message/beam recovery or beam trackingmessage comprises: selecting the resource or the waveform based at leastin part on the symbol of the selected DL beam.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the resource may be associatedwith one or more tones in a component carrier. In some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove, the resource may be associated with a component carrier. Someexamples of the method, apparatus, and non-transitory computer-readablemedium described above may further include processes, features, means,or instructions for selecting a combination of the resource and thewaveform to transmit the RACH message/scheduling request message/beamrecovery or beam tracking message to the base station.

A method of wireless communication is described. The method may includetransmitting a DL signal on one or more DL beams, receiving, on at leastone of a resource or a waveform, a RACH message/scheduling requestmessage/beam recovery or beam tracking message from a UE, identifying,based at least in part on the resource or the waveform, a selected DLbeam of the one or more DL beams for communications from the basestation to the UE, and transmitting one or more subsequent messages tothe UE using the selected DL beam.

An apparatus for wireless communication is described. The apparatus mayinclude means for transmitting a DL signal on one or more DL beams,means for receiving, on at least one of a resource or a waveform, a RACHmessage/scheduling request message/beam recovery or beam trackingmessage from a UE, means for identifying, based at least in part on theresource or the waveform, a selected DL beam of the one or more DL beamsfor communications from the base station to the UE, and means fortransmitting one or more subsequent messages to the UE using theselected DL beam.

Another apparatus for wireless communication is described. The apparatusmay include a processor, memory in electronic communication with theprocessor, and instructions stored in the memory. The instructions maybe operable to cause the processor to transmit a DL signal on one ormore DL beams, receive, on at least one of a resource or a waveform, aRACH message/scheduling request message/beam recovery or beam trackingmessage from a UE, identify, based at least in part on the resource orthe waveform, a selected DL beam of the one or more DL beams forcommunications from the base station to the UE, and transmit one or moresubsequent messages to the UE using the selected DL beam.

A non-transitory computer readable medium for wireless communication isdescribed. The non-transitory computer-readable medium may includeinstructions operable to cause a processor to transmit a DL signal onone or more DL beams, receive, on at least one of a resource or awaveform, a RACH message/scheduling request message/beam recovery orbeam tracking message from a UE, identify, based at least in part on theresource or the waveform, a selected DL beam of the one or more DL beamsfor communications from the base station to the UE, and transmit one ormore subsequent messages to the UE using the selected DL beam.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, identifying the selected DLbeam comprises: associating the resource or the waveform with an indexof the selected DL beam. In some examples of the method, apparatus, andnon-transitory computer-readable medium described above, identifying theselected DL beam comprises: associating the resource or the waveformwith a symbol of a subframe of the DL signal of the selected DL beam.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, receiving the RACHmessage/scheduling request message/beam recovery or beam trackingmessage comprises: receiving the RACH message/scheduling requestmessage/beam recovery or beam tracking message during an entire durationof a corresponding random access subframe. In some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove, receiving the RACH message/scheduling request message/beamrecovery or beam tracking message comprises: receiving the RACHmessage/scheduling request message/beam recovery or beam trackingmessage on a plurality of UL beams.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for measuring a quality of the RACHmessage/scheduling request message/beam recovery or beam trackingmessage received on the plurality of UL beams. Some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove may further include processes, features, means, or instructionsfor determining a selected UL beam for communications from the UE to thebase station based at least in part on the quality.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, measuring the quality of theRACH message/scheduling request message/beam recovery or beam trackingmessage comprises: measuring one or more of a reference signal receivedpower (RSRP), a received signal strength indicator (RSSI), a referencesignal received quality (RSRQ), a signal to noise ratio (SNR), or asignal to interference plus noise ratio (SINR). In some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove, identifying the selected DL beam further comprises: identifyingthe selected DL beam based at least in part on the resource or thewaveform of the RACH message/scheduling request message/beam recovery orbeam tracking message.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, identifying the selected DLbeam comprises: identifying the selected DL beam based at least in parton a RACH preamble of the RACH message, a cyclic shift of the RACHmessage, or combinations thereof. In some examples of the method,apparatus, and non-transitory computer-readable medium described above,a correspondence is absent between the one or more DL beams from thebase station and one or more uplink (UL) beams at the base station,wherein the absent correspondence is associated with the one or more DLbeams having different beam directions than the one or more UL receivebeams.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying that correspondence isabsent between the one or more DL beams from the base station and one ormore uplink (UL) beams at the base station. Some examples of the method,apparatus, and non-transitory computer-readable medium described abovemay further include processes, features, means, or instructions fortransmitting the indication of the absent correspondence in a MIB or aSIB.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving an indication thatcorrespondence is absent between the one or more DL beams from the basestation and one or more UL beams from the UE and mapping DL beams usedto transmit channel state information reference signals (CSI-RSs) to ULbeams used to transmit sounding reference signals (SRS) or mapping ULbeams used to transmit sounding reference signals (SRS) to DL beams usedto transmit channel state information reference signals (CSI-RSs). Someexamples of the method, apparatus, and non-transitory computer-readablemedium described above may further include processes, features, means,or instructions for receiving an indication that correspondence isabsent between the one or more DL beams from the base station and one ormore UL beams from the UE and mapping DL beams used in DL beam trainingto UL beams used in UL beam training or mapping UL beams used in UL beamtraining to DL beams used in DL beam training.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the selected DL beam from thebase station may be different from a selected UL beam from the UE. Insome examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the resource may be associatedwith one or more tones in a component carrier. In some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove, the resource may be associated with a component carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system for wireless communicationthat supports RACH conveyance of DL synchronization beam information forvarious DL-UL correspondence states in accordance with aspects of thepresent disclosure;

FIG. 2 illustrates an example of a process flow that supports RACHconveyance of DL synchronization beam information for various DL-ULcorrespondence states in accordance with aspects of the presentdisclosure;

FIG. 3 illustrates an example of a system for wireless communicationthat supports RACH conveyance of DL synchronization beam information forvarious DL-UL correspondence states in accordance with aspects of thepresent disclosure;

FIGS. 4A and 4B illustrate examples of aspects of a beam-subframemapping configuration that supports RACH conveyance of DLsynchronization beam information for various DL-UL correspondence statesin accordance with aspects of the present disclosure;

FIGS. 5A and 5B illustrate examples of a beam-subframe mappingconfiguration that supports RACH conveyance of DL synchronization beaminformation for various DL-UL correspondence states in accordance withaspects of the present disclosure;

FIGS. 6A and 6B illustrate examples of a beam-subframe mappingconfiguration that supports RACH conveyance of DL synchronization beaminformation for various DL-UL correspondence states in accordance withaspects of the present disclosure;

FIGS. 7A and 7B illustrate examples of a beam-subframe mappingconfiguration that supports RACH conveyance of DL synchronization beaminformation for various DL-UL correspondence states in accordance withaspects of the present disclosure;

FIGS. 8 through 10 show block diagrams of a device that supports RACHconveyance of DL synchronization beam information for various DL-ULcorrespondence states in accordance with aspects of the presentdisclosure;

FIG. 11 illustrates a block diagram of a system including a UE thatsupports RACH conveyance of DL synchronization beam information forvarious DL-UL correspondence states in accordance with aspects of thepresent disclosure;

FIGS. 12 through 14 show block diagrams of a device that supports RACHconveyance of DL synchronization beam information for various DL-ULcorrespondence states in accordance with aspects of the presentdisclosure;

FIG. 15 illustrates a block diagram of a system including a base stationthat supports RACH conveyance of DL synchronization beam information forvarious DL-UL correspondence states in accordance with aspects of thepresent disclosure; and

FIGS. 16 through 19 illustrate methods for RACH conveyance of DLsynchronization beam information for various DL-UL correspondence statesin accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

Free space path loss may increase with carrier frequency. Transmissionin millimeter wave (mmW) systems may also be impacted from additionalnon-line-of-sight losses, (e.g., diffraction loss, penetration loss,oxygen absorption loss, foliage loss, etc.). During initial access, thebase station and the user equipment (UE) may attempt to overcome thesehigh path losses to discover or detect each other. Aspects of thepresent disclosure provide for improved initial access in a mmW system.

Aspects of the disclosure are initially described in the context of awireless communications system. Generally, the described techniquesprovide for a UE to convey an indication to a base station of a selecteddownlink (DL) beam by selecting a corresponding resource and/or randomaccess channel (RACH) waveform for transmission of a RACHmessage/scheduling request message/beam recovery or beam trackingmessage. For example, the base station may transmit DL signal(s) on DLbeam(s). The UE may select a DL beam from the DL signal(s) that can beused for DL communications, (e.g., from the base station to the UE). TheUE may select a resource and/or a waveform (e.g., a RACH waveform or ascheduling request waveform) for transmission of the RACHmessage/scheduling request message/beam recovery or beam trackingmessage to the base station, where the selection is based on theselected DL beam. The UE may then transmit the RACH message/schedulingrequest message/beam recovery or beam tracking message to the basestation using the selected resource and/or RACH waveform. The basestation receives the RACH message/scheduling request message/beamrecovery or beam tracking message on the selected resource and/or RACHwaveform and uses the resource and/or RACH waveform to identify theselected DL beam. In one non-limiting example, the UE may select aresource (e.g., channel) that corresponds to the timing feature of theDL signal(s) (e.g., symbol). The base station may then use the selectedDL beam for communications from the base station to the UE, (e.g., forsubsequent DL communications). In some aspects, a resource may refer toa time resource, a frequency resource, a time-frequency resource, andthe like.

Aspects of the disclosure are further illustrated by and described withreference to apparatus diagrams, system diagrams, and flowcharts thatrelate to RACH conveyance of DL synchronization beam information forvarious DL-UL correspondence states. In some aspects, the termcorrespondence may refer to reciprocity.

FIG. 1 illustrates an example of a wireless communications system 100 inaccordance with various aspects of the present disclosure. The wirelesscommunications system 100 includes base stations 105, UEs 115, and acore network 130. In some examples, the wireless communications system100 may be an LTE (or LTE-Advanced) network.

Base stations 105 may wirelessly communicate with UEs 115 via one ormore base station antennas. Each base station 105 may providecommunication coverage for a respective geographic coverage area 110.Communication links 125 shown in wireless communications system 100 mayinclude UL transmissions from a UE 115 to a base station 105, or DLtransmissions, from a base station 105 to a UE 115. UEs 115 may bedispersed throughout the wireless communications system 100, and each UE115 may be stationary or mobile. A UE 115 may also be referred to as amobile station, a subscriber station, a mobile unit, a subscriber unit,a wireless unit, a remote unit, a mobile device, a wireless device, awireless communications device, a remote device, a mobile subscriberstation, an access terminal, a mobile terminal, a wireless terminal, aremote terminal, a handset, a user agent, a mobile client, a client, orsome other suitable terminology. A UE 115 may also be a cellular phone,a personal digital assistant (PDA), a wireless modem, a wirelesscommunication device, a handheld device, a tablet computer, a laptopcomputer, a cordless phone, a personal electronic device, a handhelddevice, a personal computer, a wireless local loop (WLL) station, anInternet of things (IoT) device, an Internet of Everything (IoE) device,a machine type communication (MTC) device, an appliance, an automobile,or the like.

Base stations 105 may communicate with the core network 130 and with oneanother. For example, base stations 105 may interface with the corenetwork 130 through backhaul links 132 (e.g., S1, etc.). Base stations105 may communicate with one another over backhaul links 134 (e.g., X2,etc.) either directly or indirectly (e.g., through core network 130).Base stations 105 may perform radio configuration and scheduling forcommunication with UEs 115, or may operate under the control of a basestation controller (not shown). In some examples, base stations 105 maybe macro cells, small cells, hot spots, or the like. Base stations 105may also be referred to as eNodeBs (eNBs) 105.

During an initial access procedure, also referred to as a RACHprocedure, UE 115 may transmit a RACH preamble to a base station 105.This may be known as RACH message 1. For example, the RACH preamble maybe randomly selected from a set of 64 predetermined sequences. This mayenable the base station 105 to distinguish between multiple UEs 115trying to access the system simultaneously. The base station 105 mayrespond with a random access response (RAR), or RACH message 2, thatprovides an UL resource grant, a timing advance and a temporary cellradio network temporary identity (C-RNTI). The UE 115 may then transmitan radio resource control (RRC) connection request, or RACH message 3,along with a temporary mobile subscriber identity (TMSI) (if the UE 115has previously been connected to the same wireless network) or a randomidentifier. The radio resource control (RRC) connection request may alsoindicate the reason the UE 115 is connecting to the network (e.g.,emergency, signaling, data exchange, etc.). The base station 105 mayrespond to the connection request with a contention resolution message,or RACH message 4, addressed to the UE 115, which may provide a newC-RNTI. If the UE 115 receives a contention resolution message with thecorrect identification, the UE 115 may proceed with RRC setup. If the UE115 does not receive a contention resolution message (e.g., if there isa conflict with another UE 115) the UE 115 may repeat the RACH processby transmitting a new RACH preamble.

Wireless communication system 100 may operate in an ultra-high frequency(UHF) frequency region using frequency bands from 700 MHz to 2600 MHz(2.6 GHz), although in some cases WLAN networks may use frequencies ashigh as 4 GHz. This region may also be known as the decimeter band,since the wavelengths range from approximately one decimeter to onemeter in length. UHF waves may propagate mainly by line of sight, andmay be blocked by buildings and environmental features. However, thewaves may penetrate walls sufficiently to provide service to UEs 115located indoors. Transmission of UHF waves is characterized by smallerantennas and shorter range (e.g., less than 100 km) compared totransmission using the smaller frequencies (and longer waves) of thehigh frequency (HF) or very high frequency (VHF) portion of thespectrum. In some cases, wireless communication system 100 may alsoutilize extremely high frequency (EHF) portions of the spectrum (e.g.,from 30 GHz to 300 GHz). This region may also be known as the millimeterband, since the wavelengths range from approximately one millimeter toone centimeter in length. Thus, EHF antennas may be even smaller andmore closely spaced than UHF antennas. In some cases, this mayfacilitate use of antenna arrays within a UE 115 (e.g., for directionalbeamforming). However, EHF transmissions may be subject to even greateratmospheric attenuation and shorter range than UHF transmissions.

Specifically, wireless communication system 100 may operate in mmWfrequency ranges, (e.g., 28 GHz, 40 GHz, 60 GHz, etc.). Wirelesscommunication at these frequencies may be associated with increasedsignal attenuation (e.g., path loss), which may be influenced by variousfactors, such as temperature, barometric pressure, diffraction, etc. Asa result, signal processing techniques such as beamforming (i.e.,directional transmission) may be used to coherently combine signalenergy and overcome the path loss in specific beam directions. In somecases, a device, such as a UE 115, may select a beam direction forcommunicating with a network by selecting the strongest beam from amonga number of signals transmitted by a base station 105. In one example,the signals may be DL synchronization signals (e.g., primary orsecondary synchronization signals) or DL reference signals (e.g.,channel state information reference signals (CSI-RS)) transmitted fromthe base station 105 during discovery. The discovery procedure may becell-specific, for example, may be directed in incremental directionsaround the coverage area 110 of the base station 105. The discoveryprocedure may be used, at least in certain aspects, to identify andselect beam(s) to be used for beamformed transmissions between the basestation 105 and a UE 115.

In some cases, base station antennas may be located within one or moreantenna arrays. One or more base station antennas or antenna arrays maybe collocated at an antenna assembly, such as an antenna tower. In somecases, antennas or antenna arrays associated with a base station 105 maybe located in diverse geographic locations. A base station 105 maymultiple use antennas or antenna arrays to conduct beamformingoperations for directional communications with a UE 115.

Wireless communication system 100 may be or include a multicarrier mmWwireless communication system. Broadly, aspects of wirelesscommunication system 100 may include a UE 115 and a base station 105configured to support RACH conveyance of DL synchronization beaminformation for various DL-UL correspondence states. For example, thebase station 105 may transmit DL signal(s) on DL beam(s). The UE 115 mayselect a DL beam from the DL signal(s) that can be used for DLcommunications, (e.g., from the base station 105 to the UE 115). The UE115 may select a resource and/or a RACH waveform for transmission of theRACH message to the base station 105, where the selection is based onthe selected DL beam. The UE 115 may then transmit the RACH message tothe base station 105 using the selected resource and/or RACH waveform.The base station 105 receives the RACH message on the selected resourceand/or RACH waveform and uses the resource and/or RACH waveform toidentify the selected DL beam. In one non-limiting example, the UE 115may select a resource (e.g., channel) that corresponds to the timingfeature of the DL synchronization signal(s) (e.g., symbol). The basestation 105 may then use the selected DL beam for communications fromthe base station 105 to the UE 115, (e.g., for subsequent DLcommunications).

FIG. 2 illustrates an example of a process flow 200 for RACH conveyanceof DL synchronization beam information for various DL-UL correspondencestates. Process flow 200 may implement aspects of wireless communicationsystem 100 of FIG. 1. Process flow 200 may include a UE 115-a and a basestation 105-a, which may be examples of the corresponding devices ofFIG. 1. Base station 105-a may be a mmW base station and a serving basestation for UE 115-a.

At 205, base station 105-a may transmit an indication of correspondenceassociated with DL beams at the base station side. In some aspects, thebase station 105-a may explicitly indicate correspondence to UE 115-a.For example, a bit may be dedicated to conveying the correspondenceindication. In other aspects, base station 105-a may implicitly indicatecorrespondence. For example, UE 115-a may deduce that correspondence ispresent or absent at base station 105-a from a mapping of DL beams tothe RACH resources or waveform. In one example, if the DL beams and theRACH resources are configured using time division duplexing (TDD), thenthis may indicate that the base station 105-a may have correspondence.

In some cases, base station 105-a may include the indication ofcorrespondence in a master information block (MIB) (e.g., bits reservedfor indicating correspondence) or a system information block (SIB)(e.g., bits reserved for indicating correspondence) transmitted to UE115-a. In some examples, the base station may transmit the MIB over aphysical broadcast channel (PBCH), and the base station may transmit theSIB over an extended PBCH. In some examples, the indication may be basedon a preamble format where one preamble format may convey an indicationof no correspondence, a second preamble format may convey an indicationof partial correspondence, and a third preamble format may convey andindication of full correspondence. Based on the indication ofcorrespondence, UE 115-a may determine whether there is fullcorrespondence, no correspondence, or partial correspondence (e.g., withuncertainty region 2*N+1, where N represents a number of subarrays at UE115-a or with uncertainty 2*M+1, where M represents a number of beamstransmitted by base station 105-a). If UE 115-a determines thatcorrespondence is absent, UE 115-a may select a UL beam (e.g., forcommunication with base station 105-a) that is different from the DLbeam used by base station 105-a.

Additionally or alternatively, at 205, UE 115-a may transmit anindication of correspondence associated with UL beams at the UE side.For example, UE 115-a may transmit a nature of correspondence betweenone or more receive DL synchronization beams at the UE and one or moretransmit uplink (UL) beams at the UE, the indication of correspondencein a RACH message (e.g., RACH msg 1 or RACH msg 3) or over a physicaluplink control channel (PUCCH) or a physical uplink shared channel(PUSCH). Base station 105-a may receive the indication of correspondenceat the UE side and, based on the indication, base station 105-a maydetermine to map beams used to transmit channel state informationreference signals (CSI-RSs) to beams used to transmit sounding referencesignals (SRSs) or vice versa. Additionally, base station 105-a maydetermine to map beams used in DL beam training to beams used in UL beamtraining or vice versa based on the indication.

At 210, base station 105-a may transmit (and UE 115-0 may receive) a DLsynchronization signal to UE 115-a. The DL synchronization signal may bea beamformed signal transmitted from base station 105-a on DLsynchronization beam(s). The DL synchronization signal may be associatedwith an index and/or a symbol of a subframe. The DL synchronizationsignal may be associated with a transmit power condition.

In some aspects, base station 105-a transmits a plurality of DLsynchronization signals during a synchronization subframe. Each DLsynchronization signal may be transmitted in a symbol of thesynchronization subframe, (e.g., DL synchronization signal 1 may betransmitted during symbol 1, Dl synchronization signal 2 may betransmitted during symbol 2, etc.).

At 215, UE 115-a may identify a selected DL beam of the DLsynchronization beams to use for communications from base station 105-ato UE 115-a. UE 115-a may identify the selected DL beam by identifying apreferred DL beam based on a signal strength and/or a signal quality ofthe DL synchronization signal, (e.g., high received signal strengthand/or low interference level). In some aspects, UE 115-a may identifythe selected DL beam by identifying a transmit power condition of the DLsynchronization signal on the DL synchronization beams, (e.g., atransmit power above a threshold level).

At 220, UE 115-a may select a resource and/or RACH waveform fortransmission of the RACH message to base station 105-a. The resourceand/or RACH waveform may be selected based, at least in certain aspects,on the selected DL beam, (e.g., based on the index of the selected DLbeam, based on the symbol of a subframe of the DL synchronization signalof the selected DL beam, etc.). The resource and/or RACH waveform may beassociated with tone(s) in a component carrier and/or associated with acomponent carrier.

At 225, UE 115-a may transmit a RACH message to base station 105-a. TheRACH message may be transmitted on the selected RACH resource and/orRACH waveform. The RACH message may be transmitted during an entireduration of a corresponding random access subframe, for example, duringeach symbol of the random access subframe. In some aspects, the RACHmessage may be transmitted during an entire duration of a correspondingrandom access slot, subframe, occasion, burst, burst set, and the like.Generally, these terms may refer to a time duration where the gNB sweepssome or all of its receive beams to receive RACH message(s). In someaspects, UE 115-a may select a RACH waveform for transmission of theRACH message. The RACH waveform may be selected based on the selected DLbeam and may include a RACH preamble, a cyclic shift, etc. In someaspects, UE 115-a may transmit the RACH message on a plurality of ULbeams.

At 230, base station 105-a may identify the selected DL beam. Basestation 105-a may identify the selected DL beam based on the resourceand/or RACH waveform used for the RACH message transmission. In someaspects, base station 105-a may identify the selected DL beam byassociating the resource and/or RACH waveform with an index of theselected DL beam. In some aspects, base station 105-a may identify theselected DL beam by associating the resource and/or RACH waveform with asymbol of a subframe of the DL synchronization signal of the selected DLbeam.

In some aspects, base station 105-a may identify the selected DL beambased on the RACH waveform of the RACH message. For example, basestation 105-a may identify the selected DL beam based on the RACHpreamble of the RACH message, a cyclic shift of the RACH message, etc.

At 235, base station 105-a may transmit subsequent messages to UE 115-ausing the selected DL beam. In some cases, the selected DL beam is apreferred DL beam. Moreover, in some aspects base station 105-a may usethe RACH message received from UE 115-a to determine a selected UL beamfor communications from UE 115-a to base station 105-a. For example,base station 105-a may measure a quality of the RACH message that isreceived on a plurality of UL beams and determine the selected UL beambased on the measured quality. Measuring the quality of the RACH messagemay include measuring a reference signal received power (RSRP), areceived signal strength indicator (RSSI), a reference signal receivedquality (RSRQ), a signal to noise ratio (SNR), a signal to interferencenoise ratio (SINR), etc.

In some cases, UE 115-a may measure an RSRP of a received signaltransmitted on a synchronization signal block (e.g., where a combinationof one or more synchronization signals are transmitted together in acertain direction) to identify the best signal. In cases where UE 115-ais unable to determine a strongest port associated with a certainsymbol, UE 115-a may indicate or convey a best SS block index or thepreferred DL beam to base station 105-a using different spreading codes(e.g., orthogonal cover codes (OCCs)). In some examples, base station105-a may transmit one or more additional reference signals (e.g., abeam reference signal (BRS), a mobility reference signal (MRS), etc.)inside symbols used for synchronization signals 205, and UE 115-a mayidentify a best transmission port (e.g., best downlink transmission beamID). As a result, UE 115-a may feed back the best downlink transmissionbeam ID by using different spreading codes.

If base station 105-a does not have beam correspondence, base station105-a may request UE 115-a transmit RACH in all symbols of the RACHslot. Base station 105-a may then find the best uplink reception beambased on the quality of received RACH signals. In some examples, whenbase station 105-a does not have transmit/reception beam correspondence,base station 105-a may configure an association between a downlinksignal or downlink channel and a subset of RACH resources and/or asubset of preamble indices (e.g., RACH preamble indices), which may beused to determine a downlink transmission beam (e.g., for sending Msg2).Based on a downlink measurement of received signals and thecorresponding association, UE 115-a may select the subset of RACHresources and/or the subset of RACH preamble indices. In such cases, apreamble index may comprise a preamble sequence index and an OCC index,such as in cases when OCC is supported. In some examples, a subset ofpreambles may be indicated by OCC indices.

In some aspects, correspondence may be absent between the DLsynchronization beams from base station 105-a and UL beams from UE115-a. Thus, in some examples the selected DL beam may be different fromthe selected UL beam. Aspects of the present disclosure may supportpartial or no beam correspondence between the DL transmission beams andthe UL receive beams. In the case of partial correspondence, the RACHmessage transmitted at 225 may be transmitted over a transmission timewith a center symbol corresponding to the best, (e.g., strongestreceived signal strength), DL synchronization beam or with a centersymbol corresponding to the symbol associated with the best DLsynchronization beam. Similarly, UE 115-a may determine the RACHpreamble of the RACH message at 225 based on the best DL synchronizationbeam, and UE 115-a may determine the subcarrier region used for thetransmission of the RACH message at 225 based on the best DLsynchronization beam. This may apply to frequency division duplexing(FDD) system where full beam correspondence may not be present betweenthe DL and UL. The amount of partial beam correspondence may vary fromone scenario to the next. In some examples, the absent correspondencemay be associated with different channel propagation characteristics forthe DL and the UL beams, (e.g., different transmit power levels,different angle of departure and/or arrival, etc.).

In some cases, correspondence may be present at the base station 105-a.In this case, the base station 105-a may transmit different DLsynchronization signals at different times, and the base station 105-amay receive the corresponding RACH resources simultaneously from UE115-a through a digital receiver sub-system, which may not suffer fromanalog beam constraints. In this case, a base station 105-a may requestthat the UE 115-a map DL synchronization signals to the RACH resourcesor waveforms. The base station 105-a may then analyze each receive beampath with a RACH detector.

Aspects of the present disclosure may also support beam correspondencebetween the DL transmission beams and the UL receive beams. In the casethat correspondence is present, the RACH message transmitted at 225 maybe transmitted over a transmission time that corresponds to the best DLsynchronization beam or the symbol corresponding to the best DLsynchronization beam.

FIG. 3 illustrates an example of a system 300 for wirelesscommunications that supports RACH conveyance of DL synchronization beaminformation for various DL-UL correspondence states. System 300 may bean example of aspects of wireless communication system 100 of FIG. 1.System 300 may be a mmW wireless communication system. System 300 mayinclude a UE 115-b and a base station 105-b, which may be examples ofthe corresponding devices of FIGS. 1 and 2. Broadly, system 300illustrates aspects of a discovery procedure where UE 115-b discoversbase station 105-b based on DL synchronization signals transmitted on DLsynchronization beams.

In some examples, base station 105-b may be a mmW base station thattransmits beamformed transmissions on an active beam to UE 115-b. Thetransmissions from base stations 105-b may be beamformed or directionaltransmissions that are directed towards UE 115-b.

For example, base station 105-b may transmit DL synchronization signalon DL synchronization beams 305. Base station 105-b may transmit DLsynchronization signals (e.g., for random access) in a beamformed mannerand swept through the angular coverage region (e.g., in azimuth and/orelevation). Each DL synchronization beam 305 may be transmitted in abeam sweeping operation in different directions so as to cover thecoverage area of base station 105-b. For example, DL synchronizationbeam 305-a may be transmitted in a first direction, DL synchronizationbeam 305-b may be transmitted in a second direction, DL synchronizationbeam 305-c may be transmitted in a third direction, and DLsynchronization beam 305-d may be transmitted in a fourth direction.Although system 300 shows four DL synchronization beams 305, it is to beunderstood that fewer and/or more DL synchronization beams 305 may betransmitted. Moreover, the DL synchronization beams 305 may betransmitted at differing beam widths, at different elevation angles,etc. In some aspects, DL synchronization beams 305 may be associatedwith a beam index, for example, an indicator identifying the beam.

In some aspects, DL synchronization beams 305 may also be transmittedduring different symbol periods of a synchronization subframe. Forexample, DL synchronization beam 305-a may be transmitted during a firstsymbol period (e.g., symbol 0), DL synchronization beam 305-b may betransmitted during a second symbol period (e.g., symbol 1), DLsynchronization beam 305-c may be transmitted during a third symbolperiod (e.g., symbol 2), and DL synchronization beam 305-d may betransmitted during a fourth symbol period (e.g., symbol 3). AdditionalDL synchronization beams 305 may be transmitted during other symbolperiods of the synchronization subframe.

Generally, performing the beam sweeping operation supports base station105-b determining which direction UE 115-b is located (e.g., afterreceiving response messages from UE 115-b). This supports transmissionof RACH message 2 from base station 105-b. Moreover, the beam sweepingoperation improves communications when correspondence does not holdbetween DL and UL channels, UE 115-b may select the frequency regionand/or the waveform configuration (e.g., resource and/or RACH waveform)for transmitting the random access signal (e.g., RACH message, RACHmsg1, or RACH msg3) based on the index of the best or preferred DLsynchronization signal on the DL synchronization beam 305. In somecases, UE 115-a may convey the best or preferred DL beam using an indexor identification in a RACH msg1. During the random access period, basestation 105-a may find the suitable UL beam by receiving the randomaccess signal in a sweeping manner. Base station 105-b may identify theUE 115-a selected DL beam from the resource and/or RACH waveform used(e.g., the used frequency region and/or waveform configuration) thatcontains the RACH message (e.g., RACH msg1 or RACH msg3) of the randomaccess signal.

Thus, UEs within the coverage area of base station 105-b may receive theDL synchronization signals on DL synchronization beams 305. The UE 115-bmay identify which DL synchronization signal is best, (e.g., strongestreceived signal strength, best channel quality, etc.), and identify thisas the selected DL beam. UE 115-b may then select a resource and/or RACHwaveform to use for transmission of the RACH message based on theselected DL beam, for example the preferred DL beam. In one example, theresource and/or RACH waveform used for the transmission of the RACHmessage may correspond to the symbol of the selected DL beam. In anotherexample, the RACH message may include an identification or index of thepreferred DL beam.

As one non-limiting example, there may be 16 different DL beamsavailable. Thus, UE 115-b may use four bits to convey the DL beaminformation to base station 105-b. There may be four subcarrier regions(e.g., resources) and four different RACH waveforms available for use byUE 115-b. Accordingly, UE 115-b may transmit the four bits by selectingone out of four different RACH waveforms and one out of foursubcarriers. Thus, UE 115-b may select a combination of the resource andthe RACH waveform to transmit the RACH message to base station 105-b.

Thus, in certain aspects system 300 may support UE 115-b selecting acombination of a RACH waveform and/or the resource used for its RACHmessage transmission based on one or more combinations of the index of aDL synchronization beam or a symbol of the DL synchronization subframe.UE 115-b may transmit random access signal (e.g., RACH message, RACHmsg1 or RACH msg3) during the entire duration of the random accesssubframe and/or during a portion of the random access subframe.

In some aspects, base station 105-b may determine the selected DL beamof UE 115-b from the used frequency region and/or RACH waveform thatcontains the message 1 of random access signal. Base station 105-b maydetermine the best UL receive beam by measuring the quality of thereceived signal at different uplink receiver beams. The signal qualitymay denote one or more combinations of RSRP, RSSI, RSRQ, SNR, SINR, etc.

In some aspects, UE 115-b may select the best DL synchronization signaland the frequency region of RACH and/or RACH waveform based on the indexof the best DL synchronization signal. UE 115-b may select a DLsynchronization beam 305 that satisfies a transmit power condition. UE115-b may select a RACH preamble and cyclic shift partially based on theindex of a DL synchronization beam 305.

The absence of correspondence may indicate that the best DL beam and thebest UL beam are not same.

In some aspects, UE 115-b may select a combination of RACH and theresource used for its transmission based on a symbol of the DLsynchronization subframe if the base station 105-b transmits multiplebeams using multiple antenna ports in each symbol of the synchronizationsubframe. In some aspects, the resource may denote the tones in acomponent carrier and/or a component carrier.

Although the example described with reference to FIG. 3 is directed totransmitting RACH message in a RACH subframe, this example is alsoapplicable to transmitting a scheduling request message, beam recoverymessage, or beam tracking message in a RACH subframe. In some cases, UE115 may find that the best synchronization beam was transmitted during aspecific symbol, and UE 115 may transmit a scheduling request message,beam recovery message, or beam tracking message in a frequency regionthat corresponds to the specific symbol. The frequency region may be ina different resource (or resource block) in a RACH subframe. That is, afirst portion of the resources in a RACH subframe may be allocated forRACH message transmissions, a second portion of the resources in a RACHsubframe may be allocated for scheduling request message transmissions,and a third portion of the resources in a RACH subframe may be allocatedfor beam recovery or beam tracking message transmissions.

UE 115-b may receive an indication of the subcarrier region for ascheduling request message transmission or a beam recovery or beamtracking message transmission through RRC signaling. In some cases,there may be eight (8) possible subcarrier regions. UE 115-b may alsoreceive the desired cyclic shift for the scheduling request messagetransmission or the beam recovery or beam tracking message transmissionthrough RRC signaling. In some examples, UE 115-b may use twelve (12)different cyclic shifts to generate a sequence for the schedulingrequest message transmission or the beam recovery or beam trackingmessage transmission. The number of available cyclic shifts for thescheduling request message transmission or the beam recovery or beamtracking message transmission may be greater than the number ofavailable cyclic shifts for a RACH message transmission, since a timingerror may be corrected before UE 115-b transmits the scheduling requestmessage transmission or the beam recovery or beam tracking message.Further, the transmission of the scheduling request message transmissionor the beam recovery or beam tracking message may span two (2) symbolswhich may provide additional degrees of freedom (e.g., 192 degrees offreedom in each symbol pair).

FIGS. 4A and 4B illustrate examples of a beam-subframe mappingconfiguration 400 for RACH conveyance of DL synchronization beaminformation for various DL-UL correspondence states. Configuration 400may implement aspects of wireless communication system 100, process flow200 and/or system 300 if FIGS. 1 through 3. In some aspects, aspects ofconfiguration 400 may be implemented by a base station 105 and/or a UE115, as is described with reference to FIGS. 1 through 3.

With reference to FIG. 4A, beam-subframe mapping configuration 400 mayinclude a plurality of DL synchronization signals transmitted on DLsynchronization beams 405. A base station 105 may transmit DLsynchronization signals (e.g., for random access) in a beamformed mannerand swept through the angular coverage region (e.g., in azimuth and/orelevation). Each DL synchronization beam 405 may be transmitted in abeam sweeping operation in different directions to cover the coveragearea of base station 105. For example, DL synchronization beam 405-a maybe transmitted in a first direction, DL synchronization beam 405-b maybe transmitted in a second direction, and so on. In some aspects, DLsynchronization beams 405 may be associated with a beam index, forexample, an indicator identifying the beam.

In some aspects, DL synchronization beams 405 may also be transmittedduring different symbol periods of a synchronization subframe 410. Thesynchronization subframe 410 may be associated with a time feature alongthe horizontal axis (e.g., symbols) and with a frequency feature alongthe vertical axis (e.g., frequencies or tones). For example, DLsynchronization beam 405-a may be transmitted during a first symbolperiod (e.g., symbol 0), DL synchronization beam 405-b may betransmitted during a second symbol period (e.g., symbol 1), and so onuntil DL synchronization beam 405-h is transmitted during an eighthsymbol period (e.g., symbol 7).

In some aspects, each DL synchronization signal transmitted on a DLsynchronization beam 405 may be transmitted on some or all of thefrequencies during the symbol. For example, DL synchronization beam405-a may be transmitted on frequency or tones 0-7 during symbol 0, DLsynchronization beam 405-b may be transmitted on frequency or tones 0-7during symbol 1, and so on.

Thus, base station 105 may sweep DL synchronization beams 405 in eightdirections during eight symbols of the synchronization subframe 410.

With reference to FIG. 4B, UEs 115 within the coverage area of basestation 105 may receive the DL synchronization signals on DLsynchronization beams 405. The UE 115 may identify which DLsynchronization signal is best, (e.g., strongest received signalstrength, best channel quality, etc.), and identify this as the selectedDL beam. In the example FIG. 4B, the UE 115 has identified DLsynchronization signal transmitted on DL synchronization beam 405-b asthe selected DL beam. As indicated, DL synchronization beam 405-b wastransmitted during the second symbol.

In some aspects, UE 115 may then select a resource to use fortransmission of the RACH message based on the selected DL beam andduring the RACH subframe 415. In one example, the resource used for thetransmission of the RACH message may correspond to the symbol of theselected DL beam. Thus, UE 115 may select the second resource 420 (e.g.,frequency or tone 1) as the resource for transmission of the RACHmessage. That is, UE 115 may select to the second resource 420 to conveyan indication of the DL synchronization beam transmitted during thesecond symbol as being the selected DL beam. As discussed above, UE 115may also select a RACH waveform to transmit the RACH message.

Thus, UE 115 may find that the best synchronization beam was transmittedduring the second symbol. UE 115 may transmit a RACH message in thesecond frequency region for all time slots (e.g., during all symbols ofthe RACH subframe 415). Base station 105 may find the best DL transmitbeam from the used frequency region (e.g., second resource 420) of therandom access signal (e.g., RACH message). In some examples, the RACHmessage transmission time units may be greater than the synchronizationsubframe time units due to DL-UL power differences, for example.

In some aspects, base station 105 may sweep the same eight directionsduring the same eight symbols during the RACH subframe 415. For example,base station 105 may configure one or more antenna arrays to receive theRACH message according to the same sweeping patter used to transmit theDL synchronization signal on the DL synchronization beams 405 during theRACH subframe 415.

The example described above with reference to FIG. 4 may apply to caseswhen there is no correspondence at the base station 105 for the selectedDL beam. Additionally, the example may apply to cases when there is nocorrespondence at both base station 105 and UE 115. In such cases, UE115 may identify a method to transmit using the selected DL beam basedon a link gain associated with transmissions from UE 115. In some cases,UE 115 may determine its link gain based on synchronization signalsreceived from base station 105. If UE 115 has a sufficient link gain tosatisfy a link budget, UE 115 may transmit the RACH message in a singleRACH subframe. However, if UE 115 does not have sufficient link gain tosatisfy a link budget, UE 115 may transmit the RACH message in multipleRACH subframes.

Although the example described with reference to FIGS. 4A and 4B isdirected to transmitting RACH message in RACH subframe 415, this exampleis also applicable to transmitting a scheduling request message, beamrecovery message, or beam tracking message in RACH subframe 415. In somecases, UE 115 may find that the best synchronization beam wastransmitted during the second symbol, and UE 115 may transmit ascheduling request message, beam recovery message, or beam trackingmessage in a second frequency region for all time slots. The secondfrequency region may be in a different resource (or resource block) inRACH subframe 415. That is, a first portion of the resources in RACHsubframe 415 may be allocated for RACH message transmissions, a secondportion of the resources in RACH subframe 415 may be allocated forscheduling request message transmissions, and a third portion of theresources in RACH subframe 415 may be allocated for beam recovery orbeam tracking message transmissions.

FIGS. 5A and 5B illustrate an example of a beam-subframe mappingconfiguration 500 for RACH conveyance of DL synchronization beaminformation for various DL-UL correspondence states. Configuration 500may implement aspects of wireless communication system 100, process flow200 and/or system 300 of FIGS. 1 through 3. In some aspects, aspects ofconfiguration 500 may be implemented by a base station 105 and/or a UE115, as is described with reference to FIGS. 1 through 3.

With reference to FIG. 5A, beam-subframe mapping configuration 500 mayinclude a plurality of DL synchronization signals transmitted on DLsynchronization beams 505. A base station 105 may transmit DLsynchronization signals (e.g., for random access) in a beamformed mannerand swept through the angular coverage region (e.g., in azimuth and/orelevation). Each DL synchronization beam 505 may be transmitted in abeam sweeping operation in different direction so as to cover thecoverage area of base station 105. For example, DL synchronization beam505-a may be transmitted in a first direction, DL synchronization beam505-b may be transmitted in a second direction, and so on. In someaspects, DL synchronization beams 505 may be associated with a beamindex, for example, an indicator identifying the beam.

In some aspects, DL synchronization beams 505 may also be transmittedduring different symbol periods of a synchronization subframe 510. Thesynchronization subframe 510 may be associated with a time feature alongthe horizontal axis (e.g., symbols) and with a frequency feature alongthe vertical axis (e.g., frequencies or tones). In the example FIG. 5A,base station 105 may be configured with four antenna arrays where basestation 105 sweeps four directions in each symbol. For example, antennaports 0-3 may be grouped into subgroup 510 and used to transmit DLsynchronization beams 505-a through 505-d during the first symbol (e.g.,symbol 0) of the synchronization subframe 510. Also, antenna ports 0-3may be grouped into subgroup 515 and used to transmit DL synchronizationbeams 505-e through 505-h during the second symbol (e.g., symbol 1) ofthe synchronization subframe 510. Thus, base station 105 may sweep eightdirections during two symbols of the synchronization subframe 510.

In some aspects, each DL synchronization signal transmitted on a DLsynchronization beam 505 may be transmitted on some or all of thefrequencies during the symbol. For example, DL synchronization beam505-a may be transmitted on any of frequency or tones 0-7 during symbol0, DL synchronization beam 505-b may be transmitted on any of frequencyor tones 0-7 during symbol 1, and so on. In some aspects, the DLsynchronization beams 505 transmitted during a symbol may not betransmitted on overlapping frequencies.

Thus, base station 105 may sweep DL synchronization beams 505 in eightdirections during eight symbols of the synchronization subframe 510.

With reference to FIG. 5B, UEs 115 within the coverage area of basestation 105 may receive the DL synchronization signals on DLsynchronization beams 505. The UE 115 may identify which DLsynchronization signal is best, (e.g., strongest received signalstrength, best channel quality, etc.), and identify this as the selectedDL beam. In the example FIG. 5B, the UE 115 has identified DLsynchronization signal transmitted on DL synchronization beam 505-a asthe selected DL beam. As indicated, DL synchronization beam 505-a wastransmitted during the first symbol (e.g., during symbol 0).

In some aspects, UE 115 may then select a resource to use fortransmission of the RACH message based on the selected DL beam andduring the RACH subframe 515. In one example, the resource used for thetransmission of the RACH message may correspond to the symbol of theselected DL beam. Thus, UE 115 may select the first resource 520 (e.g.,frequency or tone 0) as the resource for transmission of the RACHmessage. That is, UE 115 may select to the first resource 520 to conveyan indication of the DL synchronization beam transmitted during thefirst symbol as being the selected DL beam.

Thus, UE 115 may find that the best synchronization beam was transmittedduring the first symbol. UE 115 may transmit a RACH message in the firstfrequency region for all time slots (e.g., during all symbols of theRACH subframe 515). Base station 105 may find the best UL received beamby measuring the quality of the received signal during different timeslots (e.g., during different symbols). In some aspects, base station105 may find the best course DL beam from the used frequency region(e.g., first resource 520) of the random access signal (e.g., RACHmessage).

In some aspects, base station 105 may sweep the same eight directionsduring the same eight symbols during the RACH subframe 515. For example,base station 105 may configure one or more antenna arrays to receive theRACH message according to the same sweeping patter used to transmit theDL synchronization signal on the DL synchronization beams 505 during thesynchronization subframe 510.

FIGS. 6A and 6B illustrate examples of a beam-subframe mappingconfiguration 600 for RACH conveyance of DL synchronization beaminformation for various DL-UL correspondence states. Configuration 600may implement aspects of wireless communication system 100, process flow200 and/or system 300 if FIGS. 1 through 3. In some aspects, aspects ofconfiguration 600 may be implemented by a base station 105 and/or a UE115, as is described with reference to FIGS. 1 through 3.

With reference to FIG. 6A, beam-subframe mapping configuration 600 mayinclude a plurality of DL synchronization signals transmitted on DLsynchronization beams 605. A base station 105 may transmit DLsynchronization signals (e.g., for random access) in a beamformed mannerand swept through the angular coverage region (e.g., in azimuth and/orelevation). Each DL synchronization beam 605 may be transmitted in abeam sweeping operation in different directions to cover the coveragearea of base station 105. For example, DL synchronization beam 605-a maybe transmitted in a first direction, DL synchronization beam 605-b maybe transmitted in a second direction, and so on. In some aspects, DLsynchronization beams 605 may be associated with a beam index, (e.g., anindicator identifying the beam).

In some aspects, DL synchronization beams 605 may also be transmittedduring different symbol periods of a synchronization subframe 610. Thesynchronization subframe 610 may be associated with a time feature alongthe horizontal axis (e.g., symbols) and with a frequency feature alongthe vertical axis (e.g., frequencies or tones). For example, DLsynchronization beam 605-a may be transmitted during a first symbolperiod (e.g., symbol 0), DL synchronization beam 605-b may betransmitted during a second symbol period (e.g., symbol 1), and so onuntil DL synchronization beam 605-h is transmitted during an eighthsymbol period (e.g., symbol 7).

In some aspects, each DL synchronization signal transmitted on a DLsynchronization beam 605 may be transmitted on some or all of thefrequencies during the symbol. For example, DL synchronization beam605-a may be transmitted on frequency or tones 0-7 during symbol 0, DLsynchronization beam 605-b may be transmitted on frequency or tones 0-7during symbol 1, and so on.

Thus, base station 105 may sweep DL synchronization beams 605 in eightdirections during eight symbols of the synchronization subframe 610.

With reference to FIG. 6B, UEs 115 within the coverage area of basestation 105 may receive the DL synchronization signals on DLsynchronization beams 605. The UE 115 may identify which DLsynchronization signal is best, (e.g., strongest received signalstrength, best channel quality, etc.), and identify this as the selectedDL beam. In the example FIG. 6B, the UE 115 has identified DLsynchronization signal transmitted on DL synchronization beam 605-b asthe selected DL beam. As indicated, DL synchronization beam 605-b wastransmitted during the second symbol.

In some aspects, DL synchronization beam 605-b may have fullcorrespondence at base station 105 and UE 115. That is, the DLsynchronization beam 605-b may be used for transmission and reception atboth base station 105 and UE 115. Thus, UE 115 may select the DLsynchronization beam 605-b to transmit a RACH message to base station105. In some cases, UE 115 may randomly select the subcarrier region fortransmission of the RACH message to provide diversity in the presence ofmultiple UEs. In the example FIG. 6B, the UE 115 has selected subcarrier3 for the transmission of the RACH message.

In other aspects, DL synchronization beam 605-b may have fullcorrespondence at base station 105 and no correspondence at UE 115. Thatis, the DL synchronization beam 605-b may be used for transmission andreception at base station 105, but a transmission from UE 115 on DLsynchronization beam 605-b may be noisy. In such cases, UE 115 mayidentify a method to transmit using the selected DL beam based on a linkgain associated with transmissions from UE 115. In some cases, UE 115may determine its link gain based on synchronization signals receivedfrom base station 105. If UE 115 has a sufficient link gain to satisfy alink budget, UE 115 may transmit the RACH message in a single RACHsubframe. However, if UE 115 does not have sufficient link gain tosatisfy a link budget, UE 115 may transmit the RACH message in multipleRACH subframes.

Although the example described with reference to FIGS. 6A and 6B isdirected to transmitting RACH message in RACH subframe 615, this exampleis also applicable to transmitting a scheduling request message, beamrecovery message, or beam tracking message in RACH subframe 615. In somecases, UE 115 may find that the best synchronization beam wastransmitted during the second symbol, and UE 115 may transmit ascheduling request message, beam recovery message, or beam trackingmessage in a second frequency region for all time slots. The secondfrequency region may be in a different resource (or resource block) inthe second symbol. That is, a first portion of the resources in RACHsubframe 615 may be allocated for RACH message transmissions, a secondportion of the resources in RACH subframe 615 may be allocated forscheduling request message transmissions, and/or a third portion of theresources in RACH subframe 615 may be allocated for beam recovery orbeam tracking message transmissions.

FIGS. 7A and 7B illustrate examples of a beam-subframe mappingconfiguration 700 for RACH conveyance of DL synchronization beaminformation for various DL-UL correspondence states. Configuration 700may implement aspects of wireless communication system 100, process flow200 and/or system 300 if FIGS. 1 through 3. In some aspects, aspects ofconfiguration 700 may be implemented by a base station 105 and/or a UE115, as is described with reference to FIGS. 1 through 3.

With reference to FIG. 7A, beam-subframe mapping configuration 700 mayinclude a plurality of DL synchronization signals transmitted on DLsynchronization beams 705. A base station 105 may transmit DLsynchronization signals (e.g., for random access) in a beamformed mannerand swept through the angular coverage region (e.g., in azimuth and/orelevation). Each DL synchronization beam 705 may be transmitted in abeam sweeping operation in different directions to cover the coveragearea of base station 105. For example, DL synchronization beam 705-a maybe transmitted in a first direction, DL synchronization beam 705-b maybe transmitted in a second direction, and so on. In some aspects, DLsynchronization beams 705 may be associated with a beam index, forexample, an indicator identifying the beam.

In some aspects, DL synchronization beams 705 may also be transmittedduring different symbol periods of a synchronization subframe 710. Thesynchronization subframe 710 may be associated with a time feature alongthe horizontal axis (e.g., symbols) and with a frequency feature alongthe vertical axis (e.g., frequencies or tones). For example, DLsynchronization beam 705-a may be transmitted during a first symbolperiod (e.g., symbol 0), DL synchronization beam 705-b may betransmitted during a second symbol period (e.g., symbol 1), and so onuntil DL synchronization beam 705-h is transmitted during an eighthsymbol period (e.g., symbol 7).

In some aspects, each DL synchronization signal transmitted on a DLsynchronization beam 705 may be transmitted on some or all of thefrequencies during the symbol. For example, DL synchronization beam705-a may be transmitted on frequency or tones 0-7 during symbol 0, DLsynchronization beam 705-b may be transmitted on frequency or tones 0-7during symbol 1, and so on.

Thus, base station 105 may sweep DL synchronization beams 705 in eightdirections during eight symbols of the synchronization subframe 710.

With reference to FIG. 7B, UEs 115 within the coverage area of basestation 105 may receive the DL synchronization signals on DLsynchronization beams 705. The UE 115 may identify which DLsynchronization signal is best, (e.g., strongest received signalstrength, best channel quality, etc.), and identify this as the selectedDL beam. In the example FIG. 7B, the UE 115 has identified DLsynchronization signal transmitted on DL synchronization beam 705-b asthe selected DL beam. As indicated, DL synchronization beam 705-b wastransmitted during the second symbol.

In some aspects, DL synchronization beam 705-b may have partialcorrespondence at base station 105 and UE 115. That is, the DLsynchronization beam 705-b may be used for transmission and reception atboth base station 105 and UE 115 with little noise. However, it may bedesirable for UE 115 to identify a better beam (e.g., stronger signalstrength) for uplink transmission. Thus, UE 115 may transmit the RACHmessage on the symbol of the selected DL beam and symbols of adjacent DLbeams (e.g., DL synchronization beams 705-a and 705-c). In order toreceive the uplink transmission, base station 105 may sweep a portion ofthe eight directions during symbols 0, 1, and 2 in the RACH subframe715.

UE 115 may then select a resource to use for transmission of the RACHmessage based on the selected DL beam and during the RACH subframe 415.In one example, the resource used for the transmission of the RACHmessage may correspond to the symbol of the selected DL beam. Thus, UE115 may select the second resource 720 (e.g., frequency or tone 1) asthe resource for transmission of the RACH message. That is, UE 115 mayselect the second resource 720 to convey an indication of the DLsynchronization beam transmitted during the second symbol as being theselected DL beam. As discussed above, UE 115 may also select a RACHwaveform to transmit the RACH message.

Thus, UE 115 may find that the best synchronization beam was transmittedduring the second symbol. UE 115 may transmit a RACH message in thesecond frequency region for a portion of the time slots (e.g., during aportion of the symbols of the RACH subframe 715). Base station 105 mayfind the best DL transmit beam from the used frequency region (e.g.,second resource 720) of the random access signal (e.g., RACH message).In some examples, the RACH message transmission time units may begreater than the synchronization subframe time units due to DL-UL powerdifferences, for example.

Although the example described with reference to FIGS. 7A and 7B isdirected to transmitting RACH message in RACH subframe 715, this exampleis also applicable to transmitting a scheduling request message, beamrecovery message, or beam tracking message in RACH subframe 715. In somecases, UE 115 may find that the best synchronization beam wastransmitted during the second symbol, and UE 115 may transmit ascheduling request message, beam recovery message, or beam trackingmessage in a second frequency region for a portion of the symbols. Thesecond frequency region may be in a different resource (or resourceblock) in RACH subframe 715. That is, a first portion of the resourcesin RACH subframe 715 may be allocated for RACH message transmissions, asecond portion of the resources in RACH subframe 715 may be allocatedfor scheduling request message transmissions, and/or a third portion ofthe resources in RACH subframe 715 may be allocated for beam recovery orbeam tracking message transmissions.

FIG. 8 shows a block diagram 800 of a wireless device 805 that supportsRACH conveyance of DL synchronization beam information for various DL-ULcorrespondence states in accordance with various aspects of the presentdisclosure. Wireless device 805 may be an example of aspects of a UE 115as described with reference to FIG. 1. Wireless device 805 may includereceiver 810, UE synchronization manager 815, and transmitter 820.Wireless device 805 may also include a processor. Each of thesecomponents may be in communication with one another (e.g., via one ormore buses).

Receiver 810 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to RACHconveyance of DL synchronization beam information for various DL-ULcorrespondence states, etc.). Information may be passed on to othercomponents of the device. The receiver 810 may be an example of aspectsof the transceiver 1135 described with reference to FIG. 11.

UE synchronization manager 815 may be an example of aspects of the UEsynchronization manager 1115 described with reference to FIG. 11. UEsynchronization manager 815 may receive a DL synchronization signal froma base station on one or more DL synchronization beams, and identify aselected DL beam of the one or more DL synchronization beams forcommunications from the base station to the UE.

Transmitter 820 may transmit signals generated by other components ofthe device. In some examples, the transmitter 820 may be collocated witha receiver 810 in a transceiver module. For example, the transmitter 820may be an example of aspects of the transceiver 1135 described withreference to FIG. 11. The transmitter 820 may include a single antenna,or it may include a set of antennas. Transmitter 820 may also transmitthe RACH message/scheduling request message/beam recovery or beamtracking message to the base station using at least one of a resource ora RACH waveform selected based at least in part on the selected DL beam.In some cases, transmitting the RACH message/scheduling requestmessage/beam recovery or beam tracking message includes: transmittingthe RACH message/scheduling request message/beam recovery or beamtracking message during an entire duration of a corresponding randomaccess subframe.

FIG. 9 shows a block diagram 900 of a wireless device 905 that supportsRACH conveyance of DL synchronization beam information for various DL-ULcorrespondence states in accordance with various aspects of the presentdisclosure. Wireless device 905 may be an example of aspects of awireless device 805 or a UE 115 as described with reference to FIGS. 1and 8. Wireless device 905 may include receiver 910, UE synchronizationmanager 915, and transmitter 920. Wireless device 905 may also include aprocessor. Each of these components may be in communication with oneanother (e.g., via one or more buses).

Receiver 910 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to RACHconveyance of DL synchronization beam information for various DL-ULcorrespondence states, etc.). Information may be passed on to othercomponents of the device. The receiver 910 may be an example of aspectsof the transceiver 1135 described with reference to FIG. 11.

UE synchronization manager 915 may be an example of aspects of the UEsynchronization manager 1115 described with reference to FIG. 11. UEsynchronization manager 915 may also include synchronization signalcomponent 925, beam selection component 930, and resource selectioncomponent 935.

Synchronization signal component 925 may receive a DL synchronizationsignal from a base station on one or more DL synchronization beams. Insome cases, a correspondence is absent between the one or more DLsynchronization beams from the base station and one or more UL receivebeams at the base station. In some cases, the one or more DLsynchronization beams are within a single symbol of a synchronizationsubframe, where selecting the resource and/or RACH waveform fortransmission of the RACH message/scheduling request message/beamrecovery or beam tracking message includes: selecting the resourceand/or RACH waveform based on the symbol of the selected DL beam.

Beam selection component 930 may identify a selected DL beam of the oneor more DL synchronization beams for communications from the basestation to the UE. In some cases, identifying the selected DL beamincludes: identifying the DL beam based on the DL synchronization signalon the one or more DL synchronization beams meeting a transmit powercondition. In some cases, the selected DL beam from the base station isdifferent from a selected UL beam from the UE. In some cases, a basestation may identify a preferred UL beam based on the quality of areceived RACH message. The base station may also transmit one or moresubsequent messages to the UE conveying an indication of the preferredUL beam.

Resource selection component 935 may select a resource and/or RACHwaveform for transmission of a RACH message/scheduling requestmessage/beam recovery or beam tracking message to the base station, theresource and/or RACH waveform being selected based on the selected DLbeam. In some cases, selecting the resource and/or RACH waveformincludes: selecting the resource and/or RACH waveform based on an indexof the selected DL beam. In some cases, selecting the resource and/orRACH waveform includes: selecting the resource and/or RACH waveformbased on a symbol of a subframe of the DL synchronization signal of theselected DL beam. In some cases, the resource is associated with one ormore tones in a component carrier. In some cases, the resource isassociated with a component carrier.

Transmitter 920 may transmit signals generated by other components ofthe device. In some examples, the transmitter 920 may be collocated witha receiver 910 in a transceiver module. For example, the transmitter 920may be an example of aspects of the transceiver 1135 described withreference to FIG. 11. The transmitter 920 may include a single antenna,or it may include a set of antennas.

FIG. 10 shows a block diagram 1000 of a UE synchronization manager 1015that supports RACH conveyance of DL synchronization beam information forvarious DL-UL correspondence states in accordance with various aspectsof the present disclosure. The UE synchronization manager 1015 may be anexample of aspects of a UE synchronization manager 815, a UEsynchronization manager 915, or a UE synchronization manager 1115described with reference to FIGS. 8, 9, and 11. The UE synchronizationmanager 1015 may include synchronization signal component 1020, beamselection component 1025, resource selection component 1030, preferredbeam component 1035, RACH waveform component 1040, and correspondencemanagement component 1045. Each of these modules may communicate,directly or indirectly, with one another (e.g., via one or more buses).

Synchronization signal component 1020 may receive a DL synchronizationsignal from a base station on one or more DL synchronization beams. Beamselection component 1025 may identify a selected DL beam of the one ormore DL synchronization beams for communications from the base stationto the UE. Resource selection component 1030 may select a resourceand/or RACH waveform for transmission of a RACH message/schedulingrequest message/beam recovery or beam tracking message to the basestation, the resource and/or RACH waveform being selected based on theselected DL beam. In some cases, the resource selection component 1030may select a resource and/or RACH waveform for transmission of a RACHmessage/scheduling request message/beam recovery or beam trackingmessage to the base station based on an indication that correspondenceis absent between the one or more DL synchronization beams from the basestation and one or more UL receive beams at the base station.

Preferred beam component 1035 may identify a preferred beam from anumber of beams transmitted by a base station. In some cases,identifying the selected DL beam includes: identifying a preferred DLbeam based on a signal strength of the DL synchronization signal on theone or more DL synchronization beams, a signal quality of the DLsynchronization signal on the one or more DL synchronization beams, orcombinations thereof. RACH waveform component 1040 may select a RACHwaveform for transmission of the RACH message/scheduling requestmessage/beam recovery or beam tracking message to the base station, theRACH waveform being selected based on the selected DL beam. In somecases, selecting the RACH waveform includes: selecting a RACH preamble,a cyclic shift, or combinations thereof based on an index of theselected DL beam.

Correspondence management component 1045 may receive an indication thatcorrespondence is absent between the one or more DL synchronizationbeams from the base station and one or more UL receive beams at the basestation. In some cases, correspondence management component 1045 maytransmit the RACH message/scheduling request message/beam recovery orbeam tracking message to the base station during an entire duration of aRACH subframe based at least in part on the indication of the absentcorrespondence. In some cases, correspondence management component 1045may receive the indication in a MIB or a SIB. In some cases,correspondence management component 1045 may transmit an indication thatcorrespondence is absent between the one or more DL synchronizationbeams from the base station and one or more UL receive beams at the basestation. In some cases, correspondence management component 1045 maytransmit the RACH message/scheduling request message/beam recovery orbeam tracking message to the base station during a first symbol of afirst random access subframe and a second symbol of a second randomaccess subframe. In some cases, correspondence management component 1045may transmit the indication of the absent correspondence of a UE in aRACH message 3, PUCCH, or a PUSCH.

In some cases, correspondence management component 1045 may receive anindication of a nature of correspondence between the one or more DLsynchronization beams from the base station and one or more UL beamsfrom the UE. In some cases, the nature of correspondence corresponds toone of: full correspondence, partial correspondence, or nocorrespondence. In some cases, correspondence management component 1045may determine that correspondence is present and select a transmissiontime for transmitting the RACH message/scheduling request message/beamrecovery or beam tracking message to the base station based on thepresent correspondence. In some cases, the transmission time includes asymbol of a corresponding random access subframe. In some cases,correspondence management component 1045 may determine that there ispartial correspondence and select a transmission time for transmittingthe RACH message/scheduling request message/beam recovery or beamtracking message to the base station based on the partialcorrespondence. In some cases, the transmission time includes multiplesymbols of a corresponding random access subframe. In some cases, a UEmay transmit multiple RACH messages if there is no beam correspondenceat UE.

In some cases, correspondence management component 1045 may select atransmission time, a frequency range, and a RACH preamble fortransmitting the RACH message based on the nature of correspondence. Insome cases, correspondence management component 1045 may select theresource or RACH waveform based at least in part on a symbol associatedwith the DL synchronization signal and the indication of the nature ofcorrespondence. In some cases, correspondence management component 1045may receive the indication of the nature of correspondence over a PBCHor an ePBCH. In some cases, correspondence management component 1045 mayreceive the indication of the nature of correspondence in a MIB or aSIB.

FIG. 11 shows a diagram of a system 1100 including a device 1105 thatsupports RACH conveyance of DL synchronization beam information forvarious DL-UL correspondence states in accordance with various aspectsof the present disclosure. Device 1105 may be an example of or includethe components of wireless device 805, wireless device 905, or a UE 115as described above, for example, with reference to FIGS. 1, 8 and 9.Device 1105 may include components for bi-directional voice and datacommunications including components for transmitting and receivingcommunications, including UE synchronization manager 1115, processor1120, memory 1125, software 1130, transceiver 1135, antenna 1140, andI/O controller 1145. These components may be in electronic communicationvia one or more busses (e.g., bus 1110). Device 1105 may communicatewirelessly with one or more base stations 105.

Processor 1120 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a digital signal processor (DSP), a centralprocessing unit (CPU), a microcontroller, an application-specificintegrated circuit (ASIC), an field-programmable gate array (FPGA), aprogrammable logic device, a discrete gate or transistor logiccomponent, a discrete hardware component, or any combination thereof).In some cases, processor 1120 may be configured to operate a memoryarray using a memory controller. In other cases, a memory controller maybe integrated into processor 1120. Processor 1120 may be configured toexecute computer-readable instructions stored in a memory to performvarious functions (e.g., functions or tasks supporting RACH conveyanceof DL synchronization beam information for various DL-UL correspondencestates).

Memory 1125 may include random access memory (RAM) and read only memory(ROM). The memory 1125 may store computer-readable, computer-executablesoftware 1130 including instructions that, when executed, cause theprocessor to perform various functions described herein. In some cases,the memory 1125 may contain, among other things, a basic input/outputsystem (BIOS) which may control basic hardware and/or software operationsuch as the interaction with peripheral components or devices.

Software 1130 may include code to implement aspects of the presentdisclosure, including code to support RACH conveyance of DLsynchronization beam information for various DL-UL correspondencestates. Software 1130 may be stored in a non-transitorycomputer-readable medium such as system memory or other memory. In somecases, the software 1130 may not be directly executable by the processorbut may cause a computer (e.g., when compiled and executed) to performfunctions described herein.

Transceiver 1135 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 1135 may represent a wireless transceiver and maycommunicate bi-directionally with another wireless transceiver. Thetransceiver 1135 may also include a modem to modulate the packets andprovide the modulated packets to the antennas for transmission, and todemodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1140.However, in some cases the device may have more than one antenna 1140,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

I/O controller 1145 may manage input and output signals for device 1105.I/O controller 1145 may also manage peripherals not integrated intodevice 1105. In some cases, I/O controller 1145 may represent a physicalconnection or port to an external peripheral. In some cases, I/Ocontroller 1145 may utilize an operating system such as iOS®, ANDROID®,MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, or another known operatingsystem.

FIG. 12 shows a block diagram 1200 of a wireless device 1205 thatsupports RACH conveyance of DL synchronization beam information forvarious DL-UL correspondence states in accordance with various aspectsof the present disclosure. Wireless device 1205 may be an example ofaspects of a base station 105 as described with reference to FIG. 1.Wireless device 1205 may include receiver 1210, base stationsynchronization manager 1215, and transmitter 1220. Wireless device 1205may also include a processor. Each of these components may be incommunication with one another (e.g., via one or more buses).

Receiver 1210 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to RACHconveyance of DL synchronization beam information for various DL-ULcorrespondence states, etc.). Information may be passed on to othercomponents of the device. The receiver 1210 may be an example of aspectsof the transceiver 1535 described with reference to FIG. 15.

Base station synchronization manager 1215 may be an example of aspectsof the base station synchronization manager 1515 described withreference to FIG. 15. Base station synchronization manager 1215 maytransmit a DL synchronization signal on one or more DL synchronizationbeams, receive, on at least one of a resource or a RACH waveform, a RACHmessage/scheduling request message/beam recovery or beam trackingmessage from a UE, and identify, based on the resource and/or RACHwaveform, a selected DL beam of the one or more DL synchronization beamsfor communications from the base station to the UE.

Transmitter 1220 may transmit signals generated by other components ofthe device. In some examples, the transmitter 1220 may be collocatedwith a receiver 1210 in a transceiver module. For example, thetransmitter 1220 may be an example of aspects of the transceiver 1535described with reference to FIG. 15. The transmitter 1220 may include asingle antenna, or it may include a set of antennas. Transmitter 1220may also transmit one or more subsequent messages to the UE using theselected DL beam.

FIG. 13 shows a block diagram 1300 of a wireless device 1305 thatsupports RACH conveyance of DL synchronization beam information forvarious DL-UL correspondence states in accordance with various aspectsof the present disclosure. Wireless device 1305 may be an example ofaspects of a wireless device 1205 or a base station 105 as describedwith reference to FIGS. 1 and 12. Wireless device 1305 may includereceiver 1310, base station synchronization manager 1315, andtransmitter 1320. Wireless device 1305 may also include a processor.Each of these components may be in communication with one another (e.g.,via one or more buses).

Receiver 1310 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to RACHconveyance of DL synchronization beam information for various DL-ULcorrespondence states, etc.). Information may be passed on to othercomponents of the device. The receiver 1310 may be an example of aspectsof the transceiver 1535 described with reference to FIG. 15.

Base station synchronization manager 1315 may be an example of aspectsof the base station synchronization manager 1515 described withreference to FIG. 15. Base station synchronization manager 1315 may alsoinclude synchronization signal component 1325, RACH component 1330, andselected beam component 1335.

Synchronization signal component 1325 may transmit a DL synchronizationsignal on one or more DL synchronization beams. In some cases, acorrespondence is absent between the one or more DL synchronizationbeams from the base station and one or more UL receive beams at the basestation.

RACH component 1330 may receive, on a resource and/or RACH waveform, aRACH message/scheduling request message/beam recovery or beam trackingmessage from a UE. In some cases, receiving the RACH message/schedulingrequest message/beam recovery or beam tracking message includes:receiving the RACH message/scheduling request message/beam recovery orbeam tracking message during an entire duration of a correspondingrandom access subframe. In some cases, receiving the RACHmessage/scheduling request message/beam recovery or beam trackingmessage includes: receiving the RACH message/scheduling requestmessage/beam recovery or beam tracking message on a set of UL beams. Insome cases, the resource is associated with one or more tones in acomponent carrier. In some cases, the resource is associated with acomponent carrier.

Selected beam component 1335 may identify, based on the resource and/orRACH waveform, a selected DL beam of the one or more DL synchronizationbeams for communications from the base station to the UE. In some cases,identifying the selected DL beam includes: associating the resourceand/or RACH waveform with an index of the selected DL beam. In somecases, identifying the selected DL beam includes: associating theresource and/or RACH waveform with a symbol of a subframe of the DLsynchronization signal of the selected DL beam. In some cases,identifying the selected DL beam further includes: identifying theselected DL beam based on a RACH waveform of the RACH message/schedulingrequest message/beam recovery or beam tracking message. In some cases,identifying the selected DL beam includes: identifying the selected DLbeam based on a RACH preamble of the RACH message, a cyclic shift of theRACH message, or combinations thereof. In some cases, the selected DLbeam from the base station is different from a selected UL beam from theUE.

Transmitter 1320 may transmit signals generated by other components ofthe device. In some examples, the transmitter 1320 may be collocatedwith a receiver 1310 in a transceiver module. For example, thetransmitter 1320 may be an example of aspects of the transceiver 1535described with reference to FIG. 15. The transmitter 1320 may include asingle antenna, or it may include a set of antennas.

FIG. 14 shows a block diagram 1400 of a base station synchronizationmanager 1415 that supports RACH conveyance of DL synchronization beaminformation for various DL-UL correspondence states in accordance withvarious aspects of the present disclosure. The base stationsynchronization manager 1415 may be an example of aspects of a basestation synchronization manager 1515 described with reference to FIGS.12, 13, and 15. The base station synchronization manager 1415 mayinclude synchronization signal component 1420, RACH component 1425,selected beam component 1430, quality measurement component 1435, ULbeam component 1440, and correspondence management component 1445. Eachof these modules may communicate, directly or indirectly, with oneanother (e.g., via one or more buses).

Synchronization signal component 1420 may transmit a DL synchronizationsignal on one or more DL synchronization beams. RACH component 1425 mayreceive, on at least one of a resource or a RACH waveform, a RACHmessage/scheduling request message/beam recovery or beam trackingmessage from a UE. Selected beam component 1430 may identify, based onthe resource and/or RACH waveform, a selected DL beam of the one or moreDL synchronization beams for communications from the base station to theUE.

Quality measurement component 1435 may measure a quality of the RACHmessage/scheduling request message/beam recovery or beam trackingmessage received on the set of UL beams. In some cases, measuring thequality of the RACH message/scheduling request message/beam recovery orbeam tracking message includes: measuring one or more of a referencesignal received power (RSRP), a received signal strength indicator(RSSI), a reference signal received quality (RSRQ), a signal to noiseratio (signal-to-noise ratio (SNR)), or a signal to interference plusnoise ratio (SINR). UL beam component 1440 may determine a selected ULbeam for communications from the UE to the base station based on thequality.

Correspondence management component 1445 may transmit an indication thatcorrespondence is absent between the one or more DL synchronizationbeams from the base station and one or more UL receive beams at the basestation. In some cases, correspondence management component 1445 maytransmit the indication in a MIB or a SIB. In some cases, correspondencemanagement component 1445 may receive an indication that correspondenceis absent between the one or more DL synchronization beams from the basestation and one or more UL receive beams at the base station and map DLbeams used to transmit CSI-RSs to UL beams used to transmit SRSs or mapUL beams used to transmit SRSs to DL beams used to transmit CSI-RSs. Insome cases, correspondence management component 1445 may receive anindication that correspondence is absent between the one or more DLsynchronization beams from the base station and one or more UL receivebeams at the base station and map DL beams used in DL beam training toUL beams used in UL beam training or map UL beams used in UL beamtraining to DL beams used in DL beam training.

FIG. 15 shows a diagram of a system 1500 including a device 1505 thatsupports RACH conveyance of DL synchronization beam information forvarious DL-UL correspondence states in accordance with various aspectsof the present disclosure. Device 1505 may be an example of or includethe components of base station 105 as described above, for example, withreference to FIG. 1. Device 1505 may include components forbi-directional voice and data communications including components fortransmitting and receiving communications, including base stationsynchronization manager 1515, processor 1520, memory 1525, software1530, transceiver 1535, antenna 1540, network communications manager1545, and base station communications manager 1550. These components maybe in electronic communication via one or more busses (e.g., bus 1510).Device 1505 may communicate wirelessly with one or more UEs 115.

Processor 1520 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, anFPGA, a programmable logic device, a discrete gate or transistor logiccomponent, a discrete hardware component, or any combination thereof).In some cases, processor 1520 may be configured to operate a memoryarray using a memory controller. In other cases, a memory controller maybe integrated into processor 1520. Processor 1520 may be configured toexecute computer-readable instructions stored in a memory to performvarious functions (e.g., functions or tasks supporting RACH conveyanceof DL synchronization beam information for various DL-UL correspondencestates).

Memory 1525 may include RAM and ROM. The memory 1525 may storecomputer-readable, computer-executable software 1530 includinginstructions that, when executed, cause the processor to perform variousfunctions described herein. In some cases, the memory 1525 may contain,among other things, a BIOS which may control basic hardware and/orsoftware operation such as the interaction with peripheral components ordevices.

Software 1530 may include code to implement aspects of the presentdisclosure, including code to support RACH conveyance of DLsynchronization beam information for various DL-UL correspondencestates. Software 1530 may be stored in a non-transitorycomputer-readable medium such as system memory or other memory. In somecases, the software 1530 may not be directly executable by the processorbut may cause a computer (e.g., when compiled and executed) to performfunctions described herein.

Transceiver 1535 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 1535 may represent a wireless transceiver and maycommunicate bi-directionally with another wireless transceiver. Thetransceiver 1535 may also include a modem to modulate the packets andprovide the modulated packets to the antennas for transmission, and todemodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1540.However, in some cases the device may have more than one antenna 1540,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

Network communications manager 1545 may manage communications with thecore network (e.g., via one or more wired backhaul links). For example,the network communications manager 1545 may manage the transfer of datacommunications for client devices, such as one or more UEs 115.

Base station communications manager 1550 may manage communications withother base station 105, and may include a controller or scheduler forcontrolling communications with UEs 115 in cooperation with other basestations 105. For example, the base station communications manager 1550may coordinate scheduling for transmissions to UEs 115 for variousinterference mitigation techniques such as beamforming or jointtransmission. In some examples, base station communications manager 1550may provide an X2 interface within an Long Term Evolution (LTE)/LTE-Awireless communication network technology to provide communicationbetween base stations 105.

FIG. 16 shows a flowchart illustrating a method 1600 for RACH conveyanceof DL synchronization beam information for various DL-UL correspondencestates in accordance with various aspects of the present disclosure. Theoperations of method 1600 may be implemented by a UE 115 or itscomponents as described herein. For example, the operations of method1600 may be performed by a UE synchronization manager as described withreference to FIGS. 8 through 11. In some examples, a UE 115 may executea set of codes to control the functional elements of the device toperform the functions described below. Additionally or alternatively,the UE 115 may perform aspects of the functions described below usingspecial-purpose hardware.

At block 1605 the UE 115 may receive a DL synchronization signal from abase station on one or more DL synchronization beams. The operations ofblock 1605 may be performed according to the methods described withreference to FIGS. 1 through 5. In certain examples, aspects of theoperations of block 1605 may be performed by a synchronization signalcomponent as described with reference to FIGS. 8 through 11.

At block 1610 the UE 115 may identify a selected DL beam of the one ormore DL synchronization beams for communications from the base stationto the UE. The operations of block 1610 may be performed according tothe methods described with reference to FIGS. 1 through 5. In certainexamples, aspects of the operations of block 1610 may be performed by abeam selection component as described with reference to FIGS. 8 through11.

At block 1615 the UE 115 may transmit the RACH message/schedulingrequest message/beam recovery or beam tracking message to the basestation using at least one of a resource or a RACH waveform selectedbased at least in part on the selected DL beam. The operations of block1615 may be performed according to the methods described with referenceto FIGS. 1 through 5. In certain examples, aspects of the operations ofblock 1615 may be performed by a transmitter as described with referenceto FIGS. 8 through 11.

FIG. 17 shows a flowchart illustrating a method 1700 for RACH conveyanceof DL synchronization beam information for various DL-UL correspondencestates in accordance with various aspects of the present disclosure. Theoperations of method 1700 may be implemented by a UE 115 or itscomponents as described herein. For example, the operations of method1700 may be performed by a UE synchronization manager as described withreference to FIGS. 8 through 11. In some examples, a UE 115 may executea set of codes to control the functional elements of the device toperform the functions described below. Additionally or alternatively,the UE 115 may perform aspects of the functions described below usingspecial-purpose hardware.

At block 1705 the UE 115 may receive a DL synchronization signal from abase station on one or more DL synchronization beams. The operations ofblock 1705 may be performed according to the methods described withreference to FIGS. 1 through 5. In certain examples, aspects of theoperations of block 1705 may be performed by a synchronization signalcomponent as described with reference to FIGS. 8 through 11.

At block 1710 the UE 115 may identify a selected DL beam of the one ormore DL synchronization beams for communications from the base stationto the UE. The operations of block 1710 may be performed according tothe methods described with reference to FIGS. 1 through 5. In certainexamples, aspects of the operations of block 1710 may be performed by abeam selection component as described with reference to FIGS. 8 through11.

At block 1715 the UE 115 may transmit the RACH message/schedulingrequest message/beam recovery or beam tracking message to the basestation using at least one of a resource or a RACH waveform selectedbased at least in part on the selected DL beam, the resource or RACHwaveform may also be selected based on an index of the selected DL beam.The operations of block 1715 may be performed according to the methodsdescribed with reference to FIGS. 1 through 5. In certain examples,aspects of the operations of block 1715 may be performed by atransmitter as described with reference to FIGS. 8 through 11.

FIG. 18 shows a flowchart illustrating a method 1800 for RACH conveyanceof DL synchronization beam information for various DL-UL correspondencestates in accordance with various aspects of the present disclosure. Theoperations of method 1800 may be implemented by a base station 105 orits components as described herein. For example, the operations ofmethod 1800 may be performed by a base station synchronization manageras described with reference to FIGS. 12 through 15. In some examples, abase station 105 may execute a set of codes to control the functionalelements of the device to perform the functions described below.Additionally or alternatively, the base station 105 may perform aspectsof the functions described below using special-purpose hardware.

At block 1805 the base station 105 may transmit a DL synchronizationsignal on one or more DL synchronization beams. The operations of block1805 may be performed according to the methods described with referenceto FIGS. 1 through 5. In certain examples, aspects of the operations ofblock 1805 may be performed by a synchronization signal component asdescribed with reference to FIGS. 12 through 15.

At block 1810 the base station 105 may receive, on at least one of aresource or a RACH waveform, a RACH message/scheduling requestmessage/beam recovery or beam tracking message from a UE. The operationsof block 1810 may be performed according to the methods described withreference to FIGS. 1 through 5. In certain examples, aspects of theoperations of block 1810 may be performed by a RACH component asdescribed with reference to FIGS. 12 through 15.

At block 1815 the base station 105 may identify, based at least in parton the resource or the RACH waveform, a selected DL beam of the one ormore DL synchronization beams for communications from the base stationto the UE. The operations of block 1815 may be performed according tothe methods described with reference to FIGS. 1 through 5. In certainexamples, aspects of the operations of block 1815 may be performed by aselected beam component as described with reference to FIGS. 12 through15.

At block 1820 the base station 105 may transmit one or more subsequentmessages to the UE using the selected DL beam. The operations of block1820 may be performed according to the methods described with referenceto FIGS. 1 through 5. In certain examples, aspects of the operations ofblock 1820 may be performed by a transmitter as described with referenceto FIGS. 12 through 15.

FIG. 19 shows a flowchart illustrating a method 1900 for RACH conveyanceof DL synchronization beam information for various DL-UL correspondencestates in accordance with various aspects of the present disclosure. Theoperations of method 1900 may be implemented by a base station 105 orits components as described herein. For example, the operations ofmethod 1900 may be performed by a base station synchronization manageras described with reference to FIGS. 12 through 15. In some examples, abase station 105 may execute a set of codes to control the functionalelements of the device to perform the functions described below.Additionally or alternatively, the base station 105 may perform aspectsof the functions described below using special-purpose hardware.

At block 1905, the base station 105 may receive, on at least one of aresource or a RACH waveform, a RACH message/scheduling requestmessage/beam recovery or beam tracking message from a UE on a pluralityof UL beams. The operations of block 1905 may be performed according tothe methods described with reference to FIGS. 1 through 5. In certainexamples, aspects of the operations of block 1905 may be performed by aRACH component as described with reference to FIGS. 12 through 15.

At block 1910 the base station 105 may measure a quality of the RACHmessage/scheduling request message/beam recovery or beam trackingmessage received on the plurality of UL beams. The operations of block1910 may be performed according to the methods described with referenceto FIGS. 1 through 5. In certain examples, aspects of the operations ofblock 1910 may be performed by a quality measurement component asdescribed with reference to FIGS. 12 through 15.

At block 1915 the base station 105 may determine or identify a selectedUL beam, for example a preferred UL beam, for communications from the UEto the base station based at least in part on the measured quality of aRACH message. The base station may also transmit one or more subsequentmessages to the UE conveying an indication of the preferred UL beam, forexample in a RACH msg2. The one or more subsequent messages to the UEmay include an identification or index of the preferred UL beam, forexample an OCC index. The operations of block 1915 may be performedaccording to the methods described with reference to FIGS. 1 through 5.In certain examples, aspects of the operations of block 1915 may beperformed by a UL beam component as described with reference to FIGS. 12through 15.

In some cases, receiving the RACH message/scheduling requestmessage/beam recovery or beam tracking message comprises: receiving theRACH message/scheduling request message/beam recovery or beam trackingmessage on a plurality of UL beams.

It should be noted that the methods described above describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Furthermore, aspects from two or more of the methods may be combined.

Techniques described herein may be used for various wirelesscommunications systems such as code division multiple access (CDMA),time division multiple access (TDMA), frequency division multiple access(FDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), and other systems.The terms “system” and “network” are often used interchangeably. A codedivision multiple access (CDMA) system may implement a radio technologysuch as CDMA2000, Universal Terrestrial Radio Access (UTRA), etc.CDMA2000 covers IS-2000, IS-95, and IS-856 standards. IS-2000 Releasesmay be commonly referred to as CDMA2000 1×, 1×, etc. IS-856 (TIA-856) iscommonly referred to as CDMA2000 1×EV-DO, High Rate Packet Data (HRPD),etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. Atime division multiple access (TDMA) system may implement a radiotechnology such as Global System for Mobile Communications (GSM).

An orthogonal frequency division multiple access (OFDMA) system mayimplement a radio technology such as Ultra Mobile Broadband (UMB),Evolved UTRA (E-UTRA), Institute of Electrical and Electronics Engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM,etc. UTRA and E-UTRA are part of Universal Mobile Telecommunicationssystem (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A)are new releases of Universal Mobile Telecommunications System (UMTS)that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, and Global System forMobile communications (GSM) are described in documents from theorganization named “3rd Generation Partnership Project” (3GPP). CDMA2000and UMB are described in documents from an organization named “3rdGeneration Partnership Project 2” (3GPP2). The techniques describedherein may be used for the systems and radio technologies mentionedabove as well as other systems and radio technologies. While aspects anLTE system may be described for purposes of example, and LTE terminologymay be used in much of the description, the techniques described hereinare applicable beyond LTE applications.

In LTE/LTE-A networks, including such networks described herein, theterm evolved node B (eNB) may be generally used to describe the basestations. The wireless communications system or systems described hereinmay include a heterogeneous LTE/LTE-A network in which different typesof eNBs provide coverage for various geographical regions. For example,each eNB or base station may provide communication coverage for a macrocell, a small cell, or other types of cell. The term “cell” may be usedto describe a base station, a carrier or component carrier associatedwith a base station, or a coverage area (e.g., sector, etc.) of acarrier or base station, depending on context.

Base stations may include or may be referred to by those skilled in theart as a base transceiver station, a radio base station, an accesspoint, a radio transceiver, a NodeB, eNodeB (eNB), Home NodeB, a HomeeNodeB, or some other suitable terminology. The geographic coverage areafor a base station may be divided into sectors making up only a portionof the coverage area. The wireless communications system or systemsdescribed herein may include base stations of different types (e.g.,macro or small cell base stations). The UEs described herein may be ableto communicate with various types of base stations and network equipmentincluding macro eNBs, small cell eNBs, relay base stations, and thelike. There may be overlapping geographic coverage areas for differenttechnologies.

A macro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by UEswith service subscriptions with the network provider. A small cell is alower-powered base station, as compared with a macro cell, that mayoperate in the same or different (e.g., licensed, unlicensed, etc.)frequency bands as macro cells. Small cells may include pico cells,femto cells, and micro cells according to various examples. A pico cell,for example, may cover a small geographic area and may allowunrestricted access by UEs with service subscriptions with the networkprovider. A femto cell may also cover a small geographic area (e.g., ahome) and may provide restricted access by UEs having an associationwith the femto cell (e.g., UEs in a closed subscriber group (CSG), UEsfor users in the home, and the like). An eNB for a macro cell may bereferred to as a macro eNB. An eNB for a small cell may be referred toas a small cell eNB, a pico eNB, a femto eNB, or a home eNB. An eNB maysupport one or multiple (e.g., two, three, four, and the like) cells(e.g., component carriers). A UE may be able to communicate with varioustypes of base stations and network equipment including macro eNBs, smallcell eNBs, relay base stations, and the like.

The wireless communications system or systems described herein maysupport synchronous or asynchronous operation. For synchronousoperation, the base stations may have similar frame timing, andtransmissions from different base stations may be approximately alignedin time. For asynchronous operation, the base stations may havedifferent frame timing, and transmissions from different base stationsmay not be aligned in time. The techniques described herein may be usedfor either synchronous or asynchronous operations.

The downlink transmissions described herein may also be called forwardlink transmissions while the uplink transmissions may also be calledreverse link transmissions. Each communication link describedherein—including, for example, wireless communications system 100 and200 of FIGS. 1 and 2—may include one or more carriers, where eachcarrier may be a signal made up of multiple sub-carriers (e.g., waveformsignals of different frequencies).

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “exemplary” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details forthe purpose of providing an understanding of the described techniques.These techniques, however, may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form in order to avoid obscuring the concepts of thedescribed examples.

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a DSP, an ASIC, an FPGA or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general-purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations. Also, as used herein, including in the claims, “or” as usedin a list of items (for example, a list of items prefaced by a phrasesuch as “at least one of” or “one or more of”) indicates an inclusivelist such that, for example, a list of at least one of A, B, or C meansA or B or C or AB or AC or BC or ABC (i.e., A and B and C). Also, asused herein, the phrase “based on” shall not be construed as a referenceto a closed set of conditions. For example, an exemplary step that isdescribed as “based on condition A” may be based on both a condition Aand a condition B without departing from the scope of the presentdisclosure. In other words, as used herein, the phrase “based on” shallbe construed in the same manner as the phrase “based at least in parton.”

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media maycomprise RAM, ROM, electrically erasable programmable read only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave are included in the definition of medium. Disk and disc,as used herein, include CD, laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notlimited to the examples and designs described herein, but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for wireless communication at a userequipment (UE), comprising: receiving a downlink (DL) signal from a basestation on one or more DL beams; identifying a selected DL beam of theone or more DL beams for communications from the base station to the UE;and transmitting a beam recovery or beam tracking message to the basestation using at least one of a resource or a waveform selected based atleast in part on the selected DL beam.
 2. The method of claim 1, whereinthe waveform comprises one of a scheduling request or a random accesschannel (RACH) waveform.
 3. The method of claim 1, wherein the DL signalcomprises a synchronization signal or a reference signal.
 4. The methodof claim 1, wherein the selected resource or waveform comprises:selecting the resource or waveform based at least in part on an index ofthe selected DL beam or a symbol of a subframe of the DL signal of theselected DL beam.
 5. The method of claim 1, wherein transmitting thebeam recovery or beam tracking message comprises: transmitting the beamrecovery or beam tracking message during an entire duration of acorresponding random access subframe.
 6. The method of claim 1, whereinidentifying the selected DL beam comprises: identifying a preferred DLbeam based at least in part on a signal strength of the DL signal on theone or more DL beams, a signal quality of the DL signal on the one ormore DL beams, or combinations thereof.
 7. The method of claim 1,wherein identifying the selected DL beam comprises: identifying the DLbeam based at least in part on the DL signal on the one or more DL beamsmeeting a transmit power condition.
 8. The method of claim 1, furthercomprising: selecting at least one of the resource or the waveform fortransmission of the beam recovery or beam tracking message to the basestation, the resource or the waveform being selected based at least inpart on the selected DL beam.
 9. The method of claim 1, wherein acorrespondence is absent between the one or more DL beams and one ormore uplink (UL) receive beams at the UE, wherein the absentcorrespondence is associated with the one or more DL beams havingdifferent beam directions than the one or more UL beams.
 10. The methodof claim 1, further comprising: identifying that correspondence isabsent between the one or more DL beams from the base station and one ormore uplink (UL) receive beams at the base station by receivinginformation from the base station in a master information block (MIB) ora system information block (SIB).
 11. The method of claim 10, furthercomprising: transmitting the beam recovery or beam tracking message tothe base station during an entire duration of a random access channel(RACH) subframe based at least in part on the identification of theabsent correspondence.
 12. The method of claim 10, further comprising:selecting the resource or waveform based at least in part on theidentification of the absent correspondence.
 13. The method of claim 1,further comprising: transmitting an indication that correspondence isabsent between the one or more DL beams from the base station and one ormore uplink (UL) beams at the UE; and transmitting the indication of theabsent correspondence in a random access channel (RACH) message 3, aphysical uplink control channel (PUCCH), or a physical uplink sharedchannel (PUSCH).
 14. The method of claim 13, further comprising:transmitting the beam recovery or beam tracking message to the basestation during a first symbol of a first random access subframe and asecond symbol of a second random access subframe.
 15. The method ofclaim 1, further comprising: receiving an indication of a nature ofcorrespondence between the one or more DL beams at the base station andone or more uplink (UL) beams at the base station, wherein the nature ofcorrespondence corresponds to one of: full correspondence, partialcorrespondence, or no correspondence.
 16. The method of claim 15,further comprising: determining that correspondence is present based onthe indication of the nature of correspondence; and selecting atransmission time for transmitting the beam recovery or beam trackingmessage to the base station based on the present correspondence, whereinthe transmission time comprises a symbol of a corresponding randomaccess subframe.
 17. The method of claim 15, further comprising:determining that there is partial correspondence based on the indicationof the nature of correspondence; and selecting a transmission time fortransmitting the beam recovery or beam tracking message to the basestation based on the partial correspondence, wherein the transmissiontime comprises multiple symbols of a corresponding random accesssubframe.
 18. The method of claim 15, further comprising: selecting theresource or waveform based at least in part on a symbol associated withthe DL signal and the indication of the nature of correspondence. 19.The method of claim 15, further comprising: receiving the indication ofthe nature of correspondence over a physical broadcast channel (PBCH) oran extended PBCH (ePBCH), or in a master information block (MIB) or asystem information block (SIB).
 20. The method of claim 1, wherein theselected DL beam from the base station is different from a selecteduplink (UL) beam from the UE.
 21. The method of claim 1, wherein the oneor more DL beams are within a single symbol of a synchronizationsubframe, wherein selecting the resource or the waveform fortransmission of the beam recovery or beam tracking message comprises:selecting the resource or the waveform based at least in part on thesymbol of the selected DL beam.
 22. The method of claim 1, wherein theresource is associated with one or more tones in a component carrier, ora component carrier, or a combination thereof.
 23. The method of claim1, further comprising: selecting a combination of the resource and thewaveform to transmit the scheduling request to the base station.
 24. Amethod for wireless communication at a base station, comprising:transmitting a downlink (DL) signal on one or more DL beams; receiving,on at least one of a resource or a waveform, a beam recovery or beamtracking message from a user equipment (UE); identifying, based at leastin part on the resource or the waveform, a selected DL beam of the oneor more DL beams for communications from the base station to the UE; andtransmitting one or more subsequent messages to the UE using theselected DL beam.
 25. The method of claim 24, wherein identifying theselected DL beam comprises: associating the resource or the waveformwith an index of the selected DL beam or with a symbol of a subframe ofthe DL signal of the selected DL beam.
 26. The method of claim 24,wherein receiving the beam recovery or beam tracking message comprises:receiving the beam recovery or beam tracking message on a plurality ofuplink (UL) beams.
 27. The method of claim 26, further comprising:measuring a quality of the beam recovery or beam tracking messagereceived on the plurality of UL beams; and determining a selected ULbeam for communications from the UE to the base station based at leastin part on the quality.
 28. The method of claim 27, wherein measuringthe quality of the beam recovery or beam tracking message comprises:measuring one or more of a reference signal received power (RSRP), areceived signal strength indicator (RSSI), a reference signal receivedquality (RSRQ), a signal to noise ratio (SNR), or a signal tointerference plus noise ratio (SINR).
 29. The method of claim 24,wherein a correspondence is absent between the one or more DL beams fromthe base station and one or more uplink (UL) beams at the base station,wherein the absent correspondence is associated with the one or more DLbeams having different beam directions than the one or more UL receivebeams.
 30. The method of claim 24, further comprising: identifying thatcorrespondence is absent between the one or more DL beams from the basestation and one or more uplink (UL) beams at the base station; andtransmitting the indication of the absent correspondence in a masterinformation block (MIB) or a system information block (SIB).